Documentation:

https://www.cisco.com/c/dam/en/us/td/docs/collaboration/webex_centers/esp/cisco_webex_meetings_it_administrator_mass_deployment_guide.pdf

Install:

Desktop App:

(autooc=0 suppresses the pre-meeting experience)

webexapp.msi AUTOOC=0 /qb-! /L*v logfile.log ALLUSERS=1

Outlook Add-in:

webexplugin.msi OFFICE=1 MSN=1 /qb-! /L*v logfile.log ALLUSERS=1 REBOOT=ReallySuppress

Even with both the App and the Add-in installed, a meeting will still request that the user install and enable an extension, per user and per browser.  Edge can be set up for zero-touch; Chrome will only require the user to enable it; Firefox does not allow any side-loading since version 74 (March 2020).

The extension can be pre-loaded with these registry keys (testing showed both were necessary).  If you're using SCCM/MEM, a Config Item will work for this.

HKLM\ Software\Policies\Microsoft\Edge\ExtensionInstallForcelist with value = ikdddppdhmjcdfgilpnbkdeggoiicjgo

AND

Same place, value = jlhmfgmfgeifomenelglieieghnjghma;https://clients2.google.com/service/update2/crx

Uninstall:

Desktop App

msiexec.exe /X{C835987A-32E5-C3F7-9314-CCFBEFFE86D0} /qb-! /L*v logfile.log ALLUSERS=1 REBOOT=ReallySuppress

Outlook Add-in

MSIEXEC.EXE /X{C509C378-2841-4553-BC72-E41E4840EEE0} /qb-! /L*v logfile.log ALLUSERS=1 REBOOT=ReallySuppress

To remove the reg keys:

REG QUERY HKLM\SOFTWARE\WOW6432Node\Google\Chrome\Extensions\jlhmfgmfgeifomenelglieieghnjghma
IF "%ERRORLEVEL%" EQU "0" REG DELETE HKLM\SOFTWARE\WOW6432Node\Google\Chrome\Extensions\jlhmfgmfgeifomenelglieieghnjghma /F

REG QUERY HKLM\SOFTWARE\Policies\Microsoft\Edge\ExtensionInstallForcelist /V 20200826
IF "%ERRORLEVEL%" EQU "0" REG DELETE HKLM\SOFTWARE\Policies\Microsoft\Edge\ExtensionInstallForcelist /V 20200826 /F

REG QUERY HKLM\SOFTWARE\Policies\Microsoft\Edge\ExtensionInstallForcelist /V 20200902
IF "%ERRORLEVEL%" EQU "0" REG DELETE HKLM\SOFTWARE\Policies\Microsoft\Edge\ExtensionInstallForcelist /V 20200902 /F