not able to upgrade to 20.04 fm 18.04 Could not calculate the upgrade An unresolvable problem occurred while calculating the upgrade.

Dear Maneli,

This message could be the result of a not completely updated situation in Ubuntu 18.04, and that therefore the current level not can be calculated.

If you are familiar in using a terminal-window, you can try to update your installation to the newest 18.04 programs.

* open a terminal window
* in this window, enter next command :

   sudo apt-get check

* your password will be asked, this is normal ; enter your password and see if there is a message about some failure.
* if the previous command was successful, then reload the 18.04-software info
* in the terminal-window enter the command :

   sudo apt-get update

* this will load information about refreshed programs in your current Ubuntu-version (18.04 / 18.10)
* bring all your current programs to the newest version ( for U-18.04 / U-18.10 ) with the command

   sudo apt-get upgrade

* Please report here what is happening if you perform these actions.

* You can close the terminal window either by the command

   exit

(or by clicking the cross in the upper right corner)

What are the results of the commands above ?
Wim

hanks a lot for your cooperation.
 Here are the results:

:~$sudo apt-get check
[sudo] password for mio:
Reading package lists... Done
Building dependency tree
Reading state information... Done
:~$ sudo apt-get update
Reading package lists... Done
:~$ sudo apt-get upgrade
Reading package lists... Done
Building dependency tree
Reading state information... Done
Calculating upgrade... Done
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.

It seems that all is OK when performing these commands. But still unable to update.
Best regards!
MO

For diagnostic purposes, what is the output of the commands

uname -a
lsb_release -crid
tail /var/log/dist-upgrade/apt.log
tail /var/log/dist-upgrade/main.log
tail /var/log/dist-upgrade/term.log

Manfred Hampl requested more information:
For diagnostic purposes, what is the output of the commands
Hi there, here's the requested info, thanks for your cooperation!

:~$ uname -a
Linux mio-System-Product-Name 4.15.0-124-generic #127-Ubuntu SMP Fri Nov 6 10:54:43 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux
:~$ lsb_release -crid
Distributor ID: Ubuntu
Description: Ubuntu 18.04.5 LTS
Release: 18.04
Codename: bionic

:~$ tail /var/log/dist-upgrade/apt.log
Broken gsettings-desktop-schemas:amd64 Breaks on mutter:amd64 < 3.28.4-0ubuntu18.04.2 | 3.36.6-1ubuntu0.20.04.2 @ii umH > (< 3.31.4)
  Considering mutter:amd64 2 as a solution to gsettings-desktop-schemas:amd64 72
  Upgrading mutter:amd64 due to Breaks field in gsettings-desktop-schemas:amd64
Investigating (9) mutter:amd64 < 3.28.4-0ubuntu18.04.2 -> 3.36.6-1ubuntu0.20.04.2 @ii umU Ib >
Broken mutter:amd64 Depends on gnome-settings-daemon-common:amd64 < none | 3.36.1-0ubuntu1 @un uH >
  Considering gnome-settings-daemon-common:amd64 0 as a solution to mutter:amd64 2
  MarkKeep mutter:amd64 < 3.28.4-0ubuntu18.04.2 -> 3.36.6-1ubuntu0.20.04.2 @ii umU Ib > FU=0
  Holding Back mutter:amd64 rather than change gnome-settings-daemon-common:amd64
Done
Log time: 2020-11-23 20:32:02.365711

:~$ tail /var/log/dist-upgrade/main.log
2020-11-23 20:30:41,760 INFO checking for python-minimal
2020-11-23 20:30:41,760 INFO installing python-is-python2 because python-minimal was installed
2020-11-23 20:30:41,760 DEBUG Installing 'python-is-python2' (python-minimal was installed on the system)
2020-11-23 20:31:58,048 ERROR Dist-upgrade failed: 'E:Error, pkgProblemResolver::Resolve generated breaks, this may be caused by held packages.'
2020-11-23 20:31:58,051 DEBUG abort called
2020-11-23 20:31:58,060 DEBUG openCache()
2020-11-23 20:32:01,939 DEBUG Comparing 4.15.0-117 with
2020-11-23 20:32:01,939 DEBUG Comparing 4.15.0-124 with 4.15.0-117
2020-11-23 20:32:01,941 DEBUG Comparing 4.15.0-70 with 4.15.0-124
2020-11-23 20:32:02,386 DEBUG /openCache(), new cache size 99501

:~$ tail /var/log/dist-upgrade/term.log
(no output here)

No help so it is solved by itself , I'll do a fresh install, thanks to all who tried to help, best!