I never thought I'd get this (in their words) "hack" from a supply chain consultant, but apparently anything is possible in 2020.  Here is a great way to run multiple desktop Teams clients at the same time.  

Copy and paste the following into a text editor:


REM Uses the file name as the profile name
ECHO - Using profile "%MSTEAMS_PROFILE%"


ECHO - Launching MS Teams with profile %MSTEAMS_PROFILE%
cd "%OLD_USERPROFILE%\AppData\Local\Microsoft\Teams"
"%OLD_USERPROFILE%\AppData\Local\Microsoft\Teams\Update.exe" --processStart "Teams.exe"

Name the file whatever you want, and give it a .cmd extension.

Now with a mere double click, I can have two desktop Teams clients open, at the same time.  In this example, I have my work account open and a guest account open for a customer: