HP Device: Proprietary Plug-in is missing

A web search for "hplip plugin download" immediately answers:

https://developers.hp.com/hp-linux-imaging-and-printing/plugins

Hmmm. Yes I tried that one and no success. Going to run hplip-3.20.5.run again. It's probably something I'm doing wrong. Maybe I should attempt to install the hplip-3.20.5-plugin.run first? We will see as that's what I am going to attempt.

Manged to run hplip-3.20.5.run.asc w/ text editor and was installed. Also ran: hplip-3.20.5-plugin.run and that was completed okay.
However ... still no functional printer after running hplip-3.20.5.run ... Will attempt to de-install - reinstall that file again and see.

I've done everything including usins hplip-3.16.10.run which did install as one would expect except that after all was done and near the end it reported two errors. 1. Python gobject/dbus may not be installed. 2. Plugin install failed! Soooo ...back to "hplip-3.20.5.run" again and I still get the message in red that I "require a binary plug-in" which I have attempted to install with "hp-setup" only to get the same message in red again and again, no matter what I do! It' still a work in 'progress'!

Adding another "hp-check-t" file report ......
paul@AsusMax-VII:~$ hp-check -t
Saving output in log file: /home/paul/hp-check.log

HP Linux Imaging and Printing System (ver. 3.20.5)
Dependency/Version Check Utility ver. 15.1

Copyright (c) 2001-18 HP Development Company, LP
This software comes with ABSOLUTELY NO WARRANTY.
This is free software, and you are welcome to distribute it
under certain conditions. See COPYING file for more details.

Note: hp-check can be run in three modes:
1. Compile-time check mode (-c or --compile): Use this mode before compiling the
HPLIP supplied tarball (.tar.gz or .run) to determine if the proper dependencies
are installed to successfully compile HPLIP.
2. Run-time check mode (-r or --run): Use this mode to determine if a distro
supplied package (.deb, .rpm, etc) or an already built HPLIP supplied tarball
has the proper dependencies installed to successfully run.
3. Both compile- and run-time check mode (-b or --both) (Default): This mode
will check both of the above cases (both compile- and run-time dependencies).

Check types:
a. EXTERNALDEP - External Dependencies
b. GENERALDEP - General Dependencies (required both at compile and run time)
c. COMPILEDEP - Compile time Dependencies
d. [All are run-time checks]
PYEXT SCANCONF QUEUES PERMISSION

Status Types:
    OK
    MISSING - Missing Dependency or Permission or Plug-in
    INCOMPAT - Incompatible dependency-version or Plugin-version

---------------
| SYSTEM INFO |
---------------

 Kernel: 5.3.0-51-generic #44~18.04.2-Ubuntu SMP Thu Apr 23 14:27:18 UTC 2020 GNU/Linux
 Host: AsusMax-VII
 Proc: 5.3.0-51-generic #44~18.04.2-Ubuntu SMP Thu Apr 23 14:27:18 UTC 2020 GNU/Linux
 Distribution: 22 19.3
 Bitness: 64 bit

-----------------------
| HPLIP CONFIGURATION |
-----------------------

HPLIP-Version: HPLIP 3.20.5
HPLIP-Home: /usr/share/hplip
HPLIP-Installation: Auto installation is supported for linuxmint distro 19.3 version

Current contents of '/etc/hp/hplip.conf' file:
# hplip.conf. Generated from hplip.conf.in by configure.

[hplip]
version=3.20.5

[dirs]
home=/usr/share/hplip
run=/var/run
ppd=/usr/share/ppd/HP
ppdbase=/usr/share/ppd
doc=/usr/share/doc/hplip-3.20.5
html=/usr/share/doc/hplip-3.20.5
icon=/usr/share/applications
cupsbackend=/usr/lib/cups/backend
cupsfilter=/usr/lib/cups/filter
drv=/usr/share/cups/drv/hp
bin=/usr/bin
apparmor=/etc/apparmor.d
# Following values are determined at configure time and cannot be changed.
[configure]
network-build=yes
libusb01-build=no
pp-build=no
gui-build=yes
scanner-build=yes
fax-build=yes
dbus-build=yes
cups11-build=no
doc-build=yes
shadow-build=no
hpijs-install=no
foomatic-drv-install=no
foomatic-ppd-install=no
foomatic-rip-hplip-install=no
hpcups-install=yes
cups-drv-install=yes
cups-ppd-install=no
internal-tag=3.20.5
restricted-build=no
ui-toolkit=qt4
qt3=no
qt4=yes
qt5=no
policy-kit=no
lite-build=no
udev_sysfs_rules=no
hpcups-only-build=no
hpijs-only-build=no
apparmor_build=yes
class-driver=no

Current contents of '/var/lib/hp/hplip.state' file:
[plugin]
installed = 1
eula = 1
version = 3.20.5

Current contents of '~/.hplip/hplip.conf' file:
[upgrade]
notify_upgrade = true
last_upgraded_time = 1589717673
pending_upgrade_time = 0

[installation]
date_time = 05/17/2020 09:16:20
version = 3.20.5

 <Package-name> <Package-Desc> <Required/Optional> <Min-Version> <Installed-Version> <Status> <Comment>

--------------
| COMPILEDEP |
--------------

 gcc gcc - GNU Project C and C++ Compiler REQUIRED - 7.5.0 OK -
 make make - GNU make utility to maintain groups of programs REQUIRED 3.0 4.1 OK -
 libtool libtool - Library building support services REQUIRED - 2.4.6 OK -

------------------------
| General Dependencies |
------------------------

 libcrypto libcrypto - OpenSSL cryptographic library REQUIRED - 1.1.1 OK -
 python-xml Python XML libraries REQUIRED - 2.2.5 OK -
 libnetsnmp-devel libnetsnmp-devel - SNMP networking library development files REQUIRED 5.0.9 5.7.3 OK -
 sane-devel SANE - Scanning library development files REQUIRED - - OK -
 pil PIL - Python Imaging Library (required for commandline scanning with hp-scan) OPTIONAL - 5.1.0 OK -
 pyqt4-dbus PyQt 4 DBus - DBus Support for PyQt4 REQUIRED 4.0 4.12.1 OK -
 libpthread libpthread - POSIX threads library REQUIRED - 2.27 OK -
 python-devel Python devel - Python development files REQUIRED 2.2 2.7.17 OK -
 cups-devel CUPS devel- Common Unix Printing System development files REQUIRED - 2.2.7 OK -
 python-dbus Python DBus - Python bindings for DBus REQUIRED 0.80.0 1.2.6 OK -
 cups-ddk CUPS DDK - CUPS driver development kit OPTIONAL - - OK -
 reportlab Reportlab - PDF library for Python OPTIONAL 2.0 3.4.0 OK -
 pyqt4 PyQt 4- Qt interface for Python (for Qt version 4.x) REQUIRED 4.0 4.12.1 OK -
 libusb libusb - USB library REQUIRED - 1.0 OK -
 cups-image CUPS image - CUPS image development files REQUIRED - 2.2.7 OK -
 python2X Python 2.2 or greater - Python programming language REQUIRED 2.2 2.7.17 OK -
 python-notify Python libnotify - Python bindings for the libnotify Desktop notifications OPTIONAL - - OK -
 libjpeg libjpeg - JPEG library REQUIRED - - OK -
 sane SANE - Scanning library REQUIRED - - OK -

----------------------
| Scan Configuration |
----------------------

 scanext Scan-SANE-Extension REQUIRED - 3.20.5 OK -
 hpaio HPLIP-SANE-Backend REQUIRED - 3.20.5 OK 'hpaio found in /etc/sane.d/dll.conf'

-------------------------
| External Dependencies |
-------------------------

 gs GhostScript - PostScript and PDF language interpreter and previewer REQUIRED 7.05 9.26 OK -
 scanimage scanimage - Shell scanning program OPTIONAL 1.0 1.0.27 OK -
 cups CUPS - Common Unix Printing System REQUIRED 1.1 2.2.7 OK 'CUPS Scheduler is running'
 network network -wget OPTIONAL - 1.19.4 OK -
 policykit PolicyKit - Administrative policy framework OPTIONAL - 0.105 OK -
 xsane xsane - Graphical scanner frontend for SANE OPTIONAL 0.9 0.999 OK -
 dbus DBus - Message bus system REQUIRED - 1.12.2 OK -
 avahi-utils avahi-utils OPTIONAL - 0.7 OK -

---------------------
| Python Extentions |
---------------------

 hpmudext IO-Extension REQUIRED - 3.20.5 OK -
 cupsext CUPS-Extension REQUIRED - 3.20.5 OK -

------------------------------
| DISCOVERED SCANNER DEVICES |
------------------------------

device `hpaio:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS' is a Hewlett-Packard HP_LaserJet_M1319f_MFP all-in-one
device `hpaio:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS' is a Hewlett-Packard HP_LaserJet_M1319f_MFP all-in-one

--------------------------
| DISCOVERED USB DEVICES |
--------------------------

  Device URI Model
  -------------------------------- ----------------------
  hp:/usb/HP_LaserJet_M1319f_MFP?s HP LaserJet M1319f MFP
  erial=N8712ZS

---------------------------------
| INSTALLED CUPS PRINTER QUEUES |
---------------------------------

HP-LaserJet-M1319f-MFP
----------------------
Type: Printer
Device URI: hp:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS
PPD: /etc/cups/ppd/HP-LaserJet-M1319f-MFP.ppd
warning: Failed to read /etc/cups/ppd/HP-LaserJet-M1319f-MFP.ppd ppd file
PPD Description:
Printer status: printer HP-LaserJet-M1319f-MFP is idle. enabled since Sat 16 May 2020 09:59:57 AM EDT
Communication status: Good

HP-LaserJet-M1319f-MFP-Fax-3
----------------------------
Type: Fax
Device URI: hpfax:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS
PPD: /etc/cups/ppd/HP-LaserJet-M1319f-MFP-Fax-3.ppd
warning: Failed to read /etc/cups/ppd/HP-LaserJet-M1319f-MFP-Fax-3.ppd ppd file
PPD Description:
Printer status: printer HP-LaserJet-M1319f-MFP-Fax-3 is idle. enabled since Fri 15 May 2020 10:44:50 AM EDT
Communication status: Good

HP_LaserJet_M1319f_MFP
----------------------
Type: Printer
Device URI: hp:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS
PPD: /etc/cups/ppd/HP_LaserJet_M1319f_MFP.ppd
warning: Failed to read /etc/cups/ppd/HP_LaserJet_M1319f_MFP.ppd ppd file
PPD Description:
Printer status: printer HP_LaserJet_M1319f_MFP is idle. enabled since Sun 17 May 2020 07:49:06 AM EDT
Communication status: Good

HP_LaserJet_M1319f_MFP_fax
--------------------------
Type: Fax
Device URI: hpfax:/usb/HP_LaserJet_M1319f_MFP?serial=N8712ZS
PPD: /etc/cups/ppd/HP_LaserJet_M1319f_MFP_fax.ppd
warning: Failed to read /etc/cups/ppd/HP_LaserJet_M1319f_MFP_fax.ppd ppd file
PPD Description:
Printer status: printer HP_LaserJet_M1319f_MFP_fax is idle. enabled since Sun 17 May 2020 07:49:06 AM EDT
Communication status: Good

--------------
| PERMISSION |
--------------

USB HP-LaserJet-M1319f-MFP Required - - OK Node:'/dev/bus/usb/003/009' Perm:' root lp rw- rw- rw- rw- r--'
No errors or warnings.

Done.
paul@AsusMax-VII:~$

warning: Failed to read /etc/cups/ppd/HP-LaserJet-M1319f-MFP.ppd ppd file

Are you member of the lp (=lineprinter) group?

And your last output does not show any message about missing plug-ins, so the plug.in apparently finally has been successfully installed.

Manfred ... I did not see in the "group file anything like "lineprinter". How would I go about just editing it and entering "lineprinter" in there or isn't it that simple?

The group is named lp which is derived from the word lineprinter.

sudo usermod -a -G lp paul

then logoff end logon again.