I don't use Ubuntu MATE 20.04 anymore, but only Ubuntu MATE 22.04. I also don't use Cisco Webex in Linux but I tried to install it just now in Ubuntu MATE 22.04 to see if I could help you. The installation completed successfully as well as starting Webex after the installation. I've mostly followed a few steps that are a bit "buried" in the "Webex App for Linux" - https://help.webex.com/en-us/article/9vstcdb/Webex-App-for-Linux - web page:
3 - Opened up a terminal and did a "cd" to that folder.
4 - Installed the package by running the following command:
sudo apt install ./Webex.deb
The installation "pulled" and installed a dependency of the libgl1-mesa-glx package automatically.
After I've done that, I got "Webex" in the list of applications in the "Accessories" menu. When I click on it, the application starts as expected (in the first execution, a window appeared to Accept some agreement) .
In case it's useful, here's the (partially snipped) output of my sudo apt install ./Webex.deb command:
$ sudo apt install ./Webex.deb
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
Note, selecting 'webex' instead of './Webex.deb'
(...)
The following additional packages will be installed:
libgl1-mesa-glx
The following NEW packages will be installed:
libgl1-mesa-glx webex
0 upgraded, 2 newly installed, 0 to remove and 36 not upgraded.
Need to get 5466 B/279 MB of archives.
After this operation, 920 MB of additional disk space will be used.
Do you want to continue? [Y/n] Y
Get:1 http://pt.archive.ubuntu.com/ubuntu jammy-updates/universe amd64 libgl1-mesa-glx amd64 22.2.5-0ubuntu0.1~22.04.1 [5466 B]
Get:2 /home/ricmarques/installers/Webex.deb webex amd64 42.12.0.24485 [279 MB]
Fetched 5466 B in 1s (3721 B/s)
Selecting previously unselected package libgl1-mesa-glx:amd64.
(Reading database ... 292983 files and directories currently installed.)
Preparing to unpack .../libgl1-mesa-glx_22.2.5-0ubuntu0.1~22.04.1_amd64.deb ...
Unpacking libgl1-mesa-glx:amd64 (22.2.5-0ubuntu0.1~22.04.1) ...
Selecting previously unselected package webex.
Preparing to unpack .../installers/Webex.deb ...
Unpacking webex (42.12.0.24485) ...
Setting up libgl1-mesa-glx:amd64 (22.2.5-0ubuntu0.1~22.04.1) ...
Setting up webex (42.12.0.24485) ...
N: Download is performed unsandboxed as root as file '/home/ricmarques/installers/Webex.deb' couldn't be accessed by user '_apt'. - pkgAcquire::Run (13: Permission denied)
Thanks Very, Very Much for your time & efforts Ricardo Dias Marques !!
I did the steps you outlined & it is showing in the menu - but still does not open.
Just to be sure I also did this:
sudo apt-get install libgl1-mesa-glx
To which the system responded:
libgl1-mesa-glx is already the newest version (21.2.6-0ubuntu0.1~20.04.2)
Most likely I should have also mentioned that he also uses Zoom & Skype to reach family members flawlessly via the same USB webcam via his HDMI display.
In the meantime Webex has offered 2 newer/bigger DEBs.
No clue what may be changing as I could find neither version info nor any changelog at their site.
All the same, tried them as they arrived, and still got the same non-response.
Maybe someday this will begin working again, but as of last night it remains a no-go.