Ubuntu Studio 22.04 shows Failed Offline Update

It seems that you try installing two packages that cannot be installed at the same time.
What is the name of the package that you want to install?

Please provide the full output that you receive for the following commands:

uname -a
lsb_release -crid
apt policy discodos
sudo dpkg --audit
sudo dpkg --configure -a

(1).
Yes Sir, This has happened while installing "DWSIM – The Open Source Chemical Process Simulator ..." package which is named as ---> "dwsim_8.3.4-amd64.deb" having size of about 146.5 MB approximately.

(2).
The output of your above mentioned commands (i.e. as per #1) are as under:
------------------------------------ OUTPUT-----------------------------------
navin@UbuntuStudio:~$ uname -a
Linux UbuntuStudio 5.15.0-57-lowlatency #63-Ubuntu SMP PREEMPT Tue Nov 29 10:18:23 UTC 2022 x86_64 x86_64 x86_64 GNU/Linux
navin@UbuntuStudio:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 22.04.1 LTS
Release: 22.04
Codename: jammy
navin@UbuntuStudio:~$ sudo dpkg --audit
[sudo] password for navin:
The following packages have been unpacked but not yet configured.
They must be configured using dpkg --configure or the configure
menu option in dselect for them to work:
 dwsim DWSIM - Open Source Process Simulator
 git fast, scalable, distributed revision control system
 git-man fast, scalable, distributed revision control system (manu
 gtk-sharp2 GTK# 2.12 suite, CLI bindings for GTK+
 inkscape vector-based drawing program
 lib2geom1.2.0:amd64 robust computational geometry framework -- shared library
 libxpm4:amd64 X11 pixmap library
 mono-complete complete Mono runtime, development tools and all librarie
 mono-roslyn Microsoft C# compiler
 mono-xsp4 simple web server to run ASP.NET 4.0 applications
 mono-xsp4-base base libraries for XSP 4.0
 monodoc-gtk2.0-manual compiled XML documentation for GTK# 2.12
 monodoc-http MonoDoc http based viewer
 monodoc-manual compiled XML documentation from the Mono project

The following packages have been triggered, but the trigger processing
has not yet been done. Trigger processing can be requested using
dselect or dpkg --configure --pending (or dpkg --triggers-only):
 desktop-file-utils Utilities for .desktop files
 hicolor-icon-theme default fallback theme for FreeDesktop.org icon themes
 libc-bin GNU C Library: Binaries
 mailcap Debian's mailcap system, and support programs
 man-db tools for reading manual pages

navin@UbuntuStudio:~$ sudo dpkg --configure -a
Setting up libxpm4:amd64 (1:3.5.12-1ubuntu0.22.04.1) ...
dpkg: dependency problems prevent configuration of mono-roslyn:
 mono-roslyn depends on mono-devel; however:
  Package mono-devel is not installed.

dpkg: error processing package mono-roslyn (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of mono-complete:
 mono-complete depends on mono-devel (= 6.12.0.182-0xamarin1+debian10b1); however:
  Package mono-devel is not installed.
 mono-complete depends on mono-roslyn (= 6.12.0.182-0xamarin1+debian10b1); however:
  Package mono-roslyn is not configured yet.

dpkg: error processing package mono-complete (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of dwsim:
 dwsim depends on mono-complete (>= 6.8); however:
  Package mono-complete is not configured yet.

dpkg: error processing package dwsim (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of mono-xsp4-base:
 mono-xsp4-base depends on mono-devel; however:
  Package mono-devel is not installed.

dpkg: error processing package mono-xsp4-base (--configure):
 dependency problems - leaving unconfigured
Setting up git-man (1:2.34.1-1ubuntu1.6) ...
Setting up lib2geom1.2.0:amd64 (1.2.2-3~bpo22.04.1~ppa1) ...
dpkg: dependency problems prevent configuration of mono-xsp4:
 mono-xsp4 depends on mono-xsp4-base (= 4.7.1-0xamarin3+debian10b1); however:
  Package mono-xsp4-base is not configured yet.

dpkg: error processing package mono-xsp4 (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of monodoc-http:
 monodoc-http depends on mono-xsp4 | mono-apache-server4 | mono-fastcgi-server4; however:
  Package mono-xsp4 is not configured yet.
  Package mono-apache-server4 is not installed.
  Package mono-fastcgi-server4 is not installed.

dpkg: error processing package monodoc-http (--configure):
 dependency problems - leaving unconfigured
Setting up inkscape (1.2.2-2ubuntu1~bpo22.04.1~ppa1) ...
Setting up git (1:2.34.1-1ubuntu1.6) ...
dpkg: dependency problems prevent configuration of monodoc-manual:
 monodoc-manual depends on monodoc-browser | monodoc-http | monodoc-viewer; however:
  Package monodoc-browser is not installed.
  Package monodoc-http is not configured yet.
  Package monodoc-viewer is not installed.
  Package monodoc-http which provides monodoc-viewer is not configured yet.

dpkg: error processing package monodoc-manual (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of monodoc-gtk2.0-manual:
 monodoc-gtk2.0-manual depends on monodoc-manual; however:
  Package monodoc-manual is not configured yet.

dpkg: error processing package monodoc-gtk2.0-manual (--configure):
 dependency problems - leaving unconfigured
dpkg: dependency problems prevent configuration of gtk-sharp2:
 gtk-sharp2 depends on monodoc-gtk2.0-manual (= 2.12.45-0xamarin19+debian10b1); however:
  Package monodoc-gtk2.0-manual is not configured yet.

dpkg: error processing package gtk-sharp2 (--configure):
 dependency problems - leaving unconfigured
Processing triggers for desktop-file-utils (0.26-1ubuntu3) ...
Processing triggers for hicolor-icon-theme (0.17-2) ...
Processing triggers for libc-bin (2.35-0ubuntu3.1) ...
Processing triggers for man-db (2.10.2-1) ...
Processing triggers for mailcap (3.70+nmu1ubuntu1) ...
Errors were encountered while processing:
 mono-roslyn
 mono-complete
 dwsim
 mono-xsp4-base
 mono-xsp4
 monodoc-http
 monodoc-manual
 monodoc-gtk2.0-manual
 gtk-sharp2
navin@UbuntuStudio:~$
------------------------------------------END OF OUTPUT--------------

The last command has already solved some of the problems.

Now please run the following command and show its output:

sudo apt install -f

The output of stuff in #3 is as under:

------------OUTPUT---------------
navin@UbuntuStudio:~$ sudo apt install -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Correcting dependencies... Done
The following packages were automatically installed and are no longer required:
  lib2geom1.1.0 libnunit-cil-dev libnunit-console-runner2.6.3-cil libnunit-core-interfaces2.6.3-cil
  libnunit-core2.6.3-cil libnunit-framework2.6.3-cil libnunit-mocks2.6.3-cil libnunit-util2.6.3-cil
  linux-headers-5.15.0-56-lowlatency linux-image-5.15.0-56-lowlatency linux-lowlatency-headers-5.15.0-56
  linux-modules-5.15.0-56-lowlatency
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
  mono-devel
The following NEW packages will be installed:
  mono-devel
0 upgraded, 1 newly installed, 0 to remove and 1 not upgraded.
9 not fully installed or removed.
Need to get 0 B/24.0 MB of archives.
After this operation, 115 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
(Reading database ... 543424 files and directories currently installed.)
Preparing to unpack .../mono-devel_6.12.0.182-0xamarin1+debian10b1_all.deb ...
Unpacking mono-devel (6.12.0.182-0xamarin1+debian10b1) ...
dpkg: error processing archive /var/cache/apt/archives/mono-devel_6.12.0.182-0xamarin1+debian10b1_all.deb (--unpack):
 trying to overwrite '/usr/bin/disco', which is also in package discodos 1.0~rc2-2
dpkg-deb: error: paste subprocess was killed by signal (Broken pipe)
Errors were encountered while processing:
 /var/cache/apt/archives/mono-devel_6.12.0.182-0xamarin1+debian10b1_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
navin@UbuntuStudio:~$
--------------END OF OUTPUT-------------

Regards.

See the output.

mono-devel version 6.12.0.182-0xamarin1+debian10b1 which is from a foreign source outside Ubuntu wants to install a file named /usr/bin/disco which is already installed by the package discodos version 1.0~rc2-2 from the Ubuntu repositories.

You cannot install both packages at the same time.

Please make up your mind which one you need and select one and delete the other.

The package mono-devel from the Ubuntu repositories does not show this problem, why are you using a foreign source?

So, should I remove the package using command:

 "sudo apt remove mono-devel:6.12.0.182-Oxamarin1+debian10b1"

in the terminal?Will it do?

(please correct the command if improper)

I am not sure whether the command will work, because of several half-installed packages, but I suggest that you try

sudo apt remove mono-devel -f

Sir,
I tried both the commands. Output is as under:
----------------------------------
1
navin@UbuntuStudio:~$ sudo apt remove mono-devel -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Package 'mono-devel' is not installed, so not removed
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 mono-complete : Depends: mono-devel (= 6.12.0.182-0xamarin1+debian10b1) but it is not going to be installed
 mono-roslyn : Depends: mono-devel but it is not going to be installed
 mono-xsp4-base : Depends: mono-devel but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$

2
navin@UbuntuStudio:~$ sudo apt remove mono-devel:6.12.0.182-Oxamarin1+debian10b1
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package mono-devel:6.12.0.182-Oxamarin1+debian10b1
E: Couldn't find any package by glob 'mono-devel:6.12.0.182-Oxamarin1+debian10b1'
navin@UbuntuStudio:~$
----------------------------------------------------------
Now, referring to the SPM (Synaptic Package Manager, following are the BROKEN and UPGRADABLE packages:
3.
In Synaptic Package Manager, there are following THREE broken dependicies

(a). mono-complete
Installed version: 6.12.0.182-Oxamarin1+debian10b1
Latest version: 6.12.0.182-Oxamarin1+debian10b1
Description; complete Mono runtime, development tools and all libraries

(b). mono roslyn
Installed version: 6.12.0.182-Oxamarin1+debian10b1
Latest version: 6.12.0.182-Oxamarin1+debian10b1
Description: Microsoft C# compiler

(c). mono-xsp4-base
Installed version: 4.7.1-Oxamarin3+debian10b1
Latest version:4.7.1-Oxamarin3+debian10b1
Description: base library for XSP4

4.
In Synaptic Package Manager, there are following FOUR Installed (upgradable) packages:

(a). libgdiplus
Installed version:6.0.4+dfsg-2
Latest version:6.0.5-Oxamarin1+debian10b1
Description: interface library for System Drawing of Mono

(b). ubuntustudio-default-settings
Installed version:22.04.26.1
Latest version:22.04.26.2
Description: default settings for the Ubuntu Studio desktop

(c). ubuntustudio-lowlatency-settings
Installed version:22.04.26.1
Latest version:22.04.26.2
Description:Adds lowlatency kernel as boot default if available

(d). ubuntustudio-performance-tweaks
Installed version:22.04.26.1
Latest version:22.04.26.2
Description:Under-the-hood tweaks for Ubuntu Studio performance

Should I completely remove all these using SPM?
... and then update and upgrade through terminal?

Please guide.
regards.

As already written in my previous comment, that command may fail (and it did).
You command was nonsense, because "apt remove" does not need a version number, and even more, you mistyped the version number.

I suggest that you try the command

navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base -f

and report the results.

For the version number: Please note that there is a difference between O and 0!

As per #9n the result is as under:
--------------------------------------------------------------
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 dwsim : Depends: mono-complete (>= 6.8) but it is not going to be installed
 mono-xsp4 : Depends: mono-xsp4-base (= 4.7.1-0xamarin3+debian10b1) but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$
------------------------------------------------------------------

regards.

Extend the command to

sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 -f

It is not giving the result. the output is as under:
-------------------------------------
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 monodoc-http : Depends: mono-xsp4 but it is not going to be installed or
                         mono-apache-server4 but it is not going to be installed or
                         mono-fastcgi-server4 but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$
----------------------------------------------

regards.

Seems to need even more parameters,

sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http -f

if you get another 'unmet dependency' error for other mono packages, then add them as well.

The process ended as under:
----------------------------------
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 monodoc-manual : Depends: monodoc-browser but it is not installable or
                           monodoc-http but it is not going to be installed or
                           monodoc-viewer
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-manual -f
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-manual monodocgtk2.0-manual -f
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package monodocgtk2.0-manual
E: Couldn't find any package by glob 'monodocgtk2.0-manual'
navin@UbuntuStudio:~$
-------------------------------------------------

You mistyped the command

sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-viewer -f

The result is as under:
------------------------------------------
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-viewer -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Virtual packages like 'monodoc-viewer' can't be removed
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 monodoc-manual : Depends: monodoc-browser but it is not installable or
                           monodoc-http but it is not going to be installed or
                           monodoc-viewer
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$
---------------------------------------------------

sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-viewer monodoc-manual -f

The output is as under:
-----------------------------------------
navin@UbuntuStudio:~$ sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-viewer monodoc-manual -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Virtual packages like 'monodoc-viewer' can't be removed
You might want to run 'apt --fix-broken install' to correct these.
The following packages have unmet dependencies:
 monodoc-gtk2.0-manual : Depends: monodoc-manual but it is not going to be installed
E: Unmet dependencies. Try 'apt --fix-broken install' with no packages (or specify a solution).
navin@UbuntuStudio:~$
----------------------------------------------

Hopefully the last missing one

sudo apt remove mono-complete mono-roslyn mono-xsp4-base dwsim mono-xsp4 monodoc-http monodoc-viewer monodoc-manual monodoc-gtk2.0-manual -f

(I see that you already tried adding monodoc-gtk2.0-manual, but you missed a quote character)

Ref:#20
Request you to indicate that where did I missed a quote character?

Q: "where did I missed a quote character?"

A: in comment #15

Instead of
sudo apt remove ... monodocgtk2.0-manual -f
it should have been
sudo apt remove ... monodoc-gtk2.0-manual -f

What is the current status?
What is the output of the commands

uname -a
lsb_release -crid
sudo dpkg --audit

Sir,
The current status is as such, no improvement.
I tried above commands.

Output is as under:
--------------------------------OUT PUT----------------
navin@UbuntuStudio:~$ sudo apt remove ... monodoc-gtk2.0-manual -f
[sudo] password for navin:
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
E: Unable to locate package ...
E: Couldn't find any package by glob '...'
navin@UbuntuStudio:~$ uname -a
Linux UbuntuStudio 5.15.0-58-lowlatency #64-Ubuntu SMP PREEMPT Fri Jan 6 03:36:28 UTC 2023 x86_64 x86_64 x86_64 GNU/Linux
navin@UbuntuStudio:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 22.04.1 LTS
Release: 22.04
Codename: jammy
navin@UbuntuStudio:~$ sudo dpkg --audit
The following packages have been unpacked but not yet configured.
They must be configured using dpkg --configure or the configure
menu option in dselect for them to work:
 dwsim DWSIM - Open Source Process Simulator
 gtk-sharp2 GTK# 2.12 suite, CLI bindings for GTK+
 mono-complete complete Mono runtime, development tools and all librarie
 mono-roslyn Microsoft C# compiler
 mono-xsp4 simple web server to run ASP.NET 4.0 applications
 mono-xsp4-base base libraries for XSP 4.0
 monodoc-gtk2.0-manual compiled XML documentation for GTK# 2.12
 monodoc-http MonoDoc http based viewer
 monodoc-manual compiled XML documentation from the Mono project
navin@UbuntuStudio:~$
---------------------- END of OUT PUT -------------------------

The issue arised after I installed an open source simulator DWSIM ( used for chemical processes ).
Should I purge it and reinstall?
OR
What else could be done.
Thanks in anticipation.

Try again with the command

sudo apt remove dwsim gtk-sharp2 mono-complete mono-roslyn mono-xsp4 mono-xsp4-base monodoc-gtk2.0-manual monodoc-http monodoc-manual

The starting point of the problem was that the packages dwsim and discodos cannot be installed at the same time, but due to the fact that dwsim is a foreign package from outside Ubuntu, Ubuntu cannot check this beforehand.

Upon applying the stuff as per #24, it is found that DWSIM was removed/uninstalled.

After that I applied few stuffs in terminal like:
dpkg --configure -a
sudo apt --fix-broken install
sudo apt list --upgradable
sudo apt autoremove
sudo apt update
sudo apt upgrade
etc. and also updated using Discover
Restarted system few times
Used SPM to update and repair broken packages.

Finally it has reached at the following status:

(1).
While reloading SPM an Error occurs with a reason as under:
W: https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.

(2).
In SPM, Installed (upgradable) shows only one package as under:
Package: libgdiplus
This package contains a GDI+ API compatible implementation needed by the System.Drawing library of Mono.

(3).
In terminal, upon updating it shows:
1 package can be upgraded. Run 'apt list --upgradable' to see it.
W: https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease: Key is sto
red in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in a
pt-key(8) for details.

But it is not getting upgraded through command or SPM. It is the same package as in (2) above.

(4).
In terminal, upon upgrading it shows:
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.

This is the status.

@Can I now reinstall DWSIM simulator? How should I proceed?
@Should I completely remove Package: libgdiplus using SPM?
@How to remove error in above (1)?

Regards....Sir.

1. for gdiplus
What output do you get for

sudo apt update
sudo apt full-upgrade
apt policy libgdiplus

2. for the warning
W: https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease: Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.

That is nonsense. You are running Ubuntu, so why do you add a repository for Debian?
In my opinion everything related to mono-project and Debian should be removed.
If you need the mono framework, then you should install the Ubuntu-provided version instead of a foreign one.

3. for dwsim
before you can install dwsim, you have to uninstall discodos, or you will run into the same problem again.

(1).
for gdiplus, I gtet the output results as under:
------------------OUTPUT-----------------------
navin@UbuntuStudio:~$ sudo apt update
[sudo] password for navin:
Hit:1 https://download.mono-project.com/repo/debian stable-buster InRelease
Hit:2 http://security.ubuntu.com/ubuntu jammy-security InRelease
Hit:3 https://ppa.launchpadcontent.net/ubuntustudio-ppa/backports/ubuntu jammy InRelease
Hit:4 http://archive.ubuntu.com/ubuntu jammy InRelease
Hit:5 http://archive.ubuntu.com/ubuntu jammy-updates InRelease
Hit:6 http://archive.ubuntu.com/ubuntu jammy-backports InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
1 package can be upgraded. Run 'apt list --upgradable' to see it.
W: https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease: Key is stored in legacy trusted.gpg ke
yring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.
navin@UbuntuStudio:~$ sudo apt full-upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
Get more security updates through Ubuntu Pro with 'esm-apps' enabled:
 libimage-magick-perl imagemagick libjs-jquery-ui libopenexr25
 libmagick++-6.q16-8 libmagickcore-6.q16-6-extra libimage-magick-q16-perl
 libmagickwand-6.q16-6 imagemagick-6.q16 libeditorconfig0
 libmagickcore-6.q16-6 imagemagick-6-common
Learn more about Ubuntu Pro at https://ubuntu.com/pro
The following packages have been kept back:
 libgdiplus
0 upgraded, 0 newly installed, 0 to remove and 1 not upgraded.
navin@UbuntuStudio:~$ apt policy libgdiplus
libgdiplus:
 Installed: 6.0.4+dfsg-2
 Candidate: 6.0.5-0xamarin1+debian10b1
 Version table:
    6.0.5-0xamarin1+debian10b1 500
       500 https://download.mono-project.com/repo/debian stable-buster/main amd64 Packages
*** 6.0.4+dfsg-2 500
       500 http://archive.ubuntu.com/ubuntu jammy/universe amd64 Packages
       100 /var/lib/dpkg/status
navin@UbuntuStudio:~$
-------------- END OF OUTPUT------------------

(2).
I respect and honour your opinio (i.e. “.....everything related to mono-project and Debian should be removed.....”). Accordingly I also feel that it is better to remove this repository and/or related files. This will remove the warning:
 “ W: https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease:
Key is stored in legacy trusted.gpg keyring (/etc/apt/trusted.gpg), see the DEPRECATION section in apt-key(8) for details.”

How can I remove this?

The Key List is as under:
--------------------------------
navin@UbuntuStudio:~$ sudo apt-key list
[sudo] password for navin:
Warning: apt-key is deprecated. Manage keyring files in trusted.gpg.d instead (see apt-key(8)).
/etc/apt/trusted.gpg
--------------------
pub   rsa2048 2014-08-04 [SC]
     3FA7 E032 8081 BFF6 A14D  A29A A6A1 9B38 D3D8 31EF
uid           [ unknown] Xamarin Public Jenkins (auto-signing) <email address hidden>
sub   rsa2048 2014-08-04 [E]

/etc/apt/trusted.gpg.d/ubuntu-keyring-2012-cdimage.gpg
------------------------------------------------------
pub   rsa4096 2012-05-11 [SC]
     8439 38DF 228D 22F7 B374  2BC0 D94A A3F0 EFE2 1092
uid           [ unknown] Ubuntu CD Image Automatic Signing Key (2012) <email address hidden>

/etc/apt/trusted.gpg.d/ubuntu-keyring-2018-archive.gpg
------------------------------------------------------
pub   rsa4096 2018-09-17 [SC]
     F6EC B376 2474 EDA9 D21B  7022 8719 20D1 991B C93C
uid           [ unknown] Ubuntu Archive Automatic Signing Key (2018) <email address hidden>

/etc/apt/trusted.gpg.d/ubuntustudio-ppa-ubuntu-backports.gpg
------------------------------------------------------------
pub   rsa4096 2019-02-07 [SC]
     1220 A5EC BA1F E99F 04CB  F741 F596 CF70 36BB AA6D
uid           [ unknown] Launchpad PPA for Ubuntu Studio PPA

navin@UbuntuStudio:~$
--------------------------

(3).
I wish to install DWSIM (if possible without any disturbance in existing os installations and apps) but for that I must uninstall discodos. Can I do it with simple “uninstall” or “purge” commands?

Regards.

Quote:
libgdiplus:
 Installed: 6.0.4+dfsg-2
 Candidate: 6.0.5-0xamarin1+debian10b1
 Version table:
    6.0.5-0xamarin1+debian10b1 500
       500 https://download.mono-project.com/repo/debian stable-buster/main amd64 Packages
*** 6.0.4+dfsg-2 500
       500 http://archive.ubuntu.com/ubuntu jammy/universe amd64 Packages
       100 /var/lib/dpkg/status
End of quote

You see that the version of libgdiplus that currently cannot be installed is coming from the mono repository for Debian.

Repeating my recommendation:
Remove all parts of mono for Debian.
I assume that the key that prodices a warning can be removed with the command

sudo apt-key del D3D831EF

You have to expect that installing/updating from the mono repository will no more work afterwards, so you have to do that together with the removal of the link to the mono repository.

And uninstalling discodos can be done with the synaptic package manager, or via command line with
sudo apt purge discodos

Thanks for the guidance. Now mainly TWO things are confusing me as under:

1.
While reloading the SPM it shows error as under:

Could not download all repository indexes

The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct.

An error occurred during the signature verification. The repository is not updated and the previous index files will be used. GPG error: https://download.mono-project.com/repo/debian stable-buster InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EFFailed to fetch https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EFSome index files failed to download. They have been ignored, or old ones used instead.

2.
Upon updating through terminal, it shows:

navin@UbuntuStudio:~$ sudo apt update
[sudo] password for navin:
Hit:1 https://download.mono-project.com/repo/debian stable-buster InRelease
Err:1 https://download.mono-project.com/repo/debian stable-buster InRelease
 The following signatures couldn't be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EF
Hit:2 http://archive.ubuntu.com/ubuntu jammy InRelease
Hit:3 http://security.ubuntu.com/ubuntu jammy-security InRelease
Hit:4 http://archive.ubuntu.com/ubuntu jammy-updates InRelease
Hit:5 http://archive.ubuntu.com/ubuntu jammy-backports InRelease
Hit:6 https://ppa.launchpadcontent.net/ubuntustudio-ppa/backports/ubuntu jammy InRelease
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
All packages are up to date.
W: An error occurred during the signature verification. The repository is not updated and the previous index files wil
l be used. GPG error: https://download.mono-project.com/repo/debian stable-buster InRelease: The following signatures
couldn't be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EF
W: Failed to fetch https://download.mono-project.com/repo/debian/dists/stable-buster/InRelease  The following signatur
es couldn't be verified because the public key is not available: NO_PUBKEY A6A19B38D3D831EF
W: Some index files failed to download. They have been ignored, or old ones used instead.
navin@UbuntuStudio:~$

3.
Upon upgrading through terminal, it shows normal.

navin@UbuntuStudio:~$ sudo apt upgrade
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Calculating upgrade... Done
The following packages were automatically installed and are no longer required:
 libgdk-pixbuf-xlib-2.0-0 libgdk-pixbuf2.0-0 libglib2.0-cil libmono-accessibility4.0-cil libmono-cairo4.0-cil
 libmono-ldap4.0-cil libmono-posix4.0-cil libmono-sqlite4.0-cil
 libmono-system-componentmodel-dataannotations4.0-cil libmono-system-data4.0-cil
 libmono-system-enterpriseservices4.0-cil libmono-system-ldap4.0-cil
 libmono-system-runtime-serialization-formatters-soap4.0-cil libmono-system-transactions4.0-cil
 libmono-system-web-applicationservices4.0-cil libmono-webbrowser4.0-cil
Use 'sudo apt autoremove' to remove them.
Get more security updates through Ubuntu Pro with 'esm-apps' enabled:
 libimage-magick-perl imagemagick libjs-jquery-ui libdcmtk16 libopenexr25
 libmagick++-6.q16-8 libmagickcore-6.q16-6-extra libimage-magick-q16-perl
 libmagickwand-6.q16-6 imagemagick-6.q16 libeditorconfig0
 libmagickcore-6.q16-6 imagemagick-6-common
Learn more about Ubuntu Pro at https://ubuntu.com/pro
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
navin@UbuntuStudio:~$

Mainly how to remove 1 & 2 (error in SPM and Updating through terminal)?
The 3 rd one seems normal as above.

regards.

Removed the links to the mono repository for Debian.
Matter normalized.
No problem while reloading the SPM
Updates and Upgrades as usual without any error or so.
 Thanks a lot for the valuable guidance and sparing your precious time for me.
Regards.
Navin Talati /27-02-2023

Thanks Manfred Hampl, that solved my question.