App “Software & Updates” not responding

I can't seem to get “Software & Updates” Application to appear after clicking on it. I don't know why. It's icon appears in the shortcut. What is the terminal command to activate this App?

I have tried this answer: “Software Updater” & “Software & Updates” not working, but it did not work.

$ uname -a
Linux Ubuntu 5.4.0-42-generic #46~18.04.1-Ubuntu SMP Fri Jul 10 07:21:24 UTC 2020 x86_64 x86_64 x86_64 GNU/Linux

$ gnome-shell --version
GNOME Shell 3.28.4

$ software-properties-gtk
ERROR:dbus.proxies:Introspect error on :1.228:/: dbus.exceptions.DBusException: org.freedesktop.DBus.Error.NoReply: Message recipient disconnected from message bus without replying
Traceback (most recent call last):
  File "/usr/bin/software-properties-gtk", line 100, in <module>
    app = SoftwarePropertiesGtk(datadir=options.data_dir, options=options, file=file)
  File "/usr/lib/python3/dist-packages/softwareproperties/gtk/SoftwarePropertiesGtk.py", line 173, in __init__
    self.backend.Reload();
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 70, in __call__
    return self._proxy_method(*args, **keywords)
  File "/usr/lib/python3/dist-packages/dbus/proxies.py", line 145, in __call__
    **keywords)
  File "/usr/lib/python3/dist-packages/dbus/connection.py", line 651, in call_blocking
    message, timeout)
dbus.exceptions.DBusException: org.freedesktop.DBus.Error.ServiceUnknown: The name :1.228 was not provided by any .service files

I also have the same msgs as in Ubuntu 18.04 software-properties-gtk failing with org.freedesktop.DBus.Error.ServiceUnknown. I used Synaptic to reinstall the package python3-size as was mentioned in this answer but to no avail.

I had also tried purging and reinstalling software-properties-gtk as was mentioned here but to no avail.

Update1:

I wonder if setuptools.py ver 50.0 broke software-properties-gtk's connection? I know that the system had this upgraded yesterday from ver 42.0.2. I just found this GitHub issue "setuptools 50 breaks pip installation" which was raised 22 hours ago. I have uninstalled it but to no avail.

Update 2: Using journalctl -e cmd in the terminal, I found this error msg:

Oct 04 08:22:14 Prime dbus-daemon[1303]: [system] Activating service name='com.ubuntu.SoftwareProperties' requested by ':1.157' (uid=1000 pid=10808 comm="/usr/bin/python3 /usr/bin/soft
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]: Unable to init server: Could not connect: Connection refused
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]: Unable to init server: Could not connect: Connection refused
Oct 04 08:22:14 Prime dbus-daemon[1303]: [system] Successfully activated service 'com.ubuntu.SoftwareProperties'
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]: Traceback (most recent call last):
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:   File "/usr/lib/software-properties/software-properties-dbus", line 68, in <module>
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:     server = SoftwarePropertiesDBus(bus, datadir=datadir)
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:   File "/usr/lib/python3/dist-packages/softwareproperties/dbus/SoftwarePropertiesDBus.py", line 66, in __init__
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:     self._livepatch_service = LivepatchService()
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:   File "/usr/lib/python3/dist-packages/softwareproperties/LivepatchService.py", line 93, in __init__
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]:     self._session = requests_unixsocket.Session()
Oct 04 08:22:14 Prime com.ubuntu.SoftwareProperties[1303]: NameError: name 'requests_unixsocket' is not defined

Also, the python package 'requests_unixsocket' is installed in the system(see below). Hence I don't understand the error msg NameError: name 'requests_unixsocket' is not defined:

$ pip list | grep requests
requests                2.24.0
requests-unixsocket     0.1.5
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/usr/bin/python3 -m pip install --upgrade pip' command.
$ pip3 list | grep requests
requests                2.24.0
requests-unixsocket     0.1.5
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/usr/bin/python3 -m pip install --upgrade pip' command.
$ pip3 list --user | grep requests
requests            2.24.0
WARNING: You are using pip version 20.2.2; however, version 20.2.3 is available.
You should consider upgrading via the '/usr/bin/python3 -m pip install --upgrade pip' command.

I have tried to import requests_unixsocket explicitly. It works. See below.

Python 3.6.9 (default, Jul 17 2020, 12:50:27) 
[GCC 8.4.0] on linux
Type "help", "copyright", "credits" or "license()" for more information.
>>> import requests_unixsocket
>>> a = requests_unixsocket.Session()
>>> a
<requests_unixsocket.Session object at 0x7fb103952470>

I don't understand why I can import the package but /usr/lib/python3/dist-packages/softwareproperties/LivepatchService.py can't see it. It does exist:

$ ls /usr/lib/python3/dist-packages/ | grep request
requests_unixsocket
requests_unixsocket-0.1.5.egg-info