I have the same problem, several employees complain, they can no longer join team meetings (same problem mentioned above).
At the beginning I thought it was from Microsoft because the simple calls work very well and on the same mac with the antivirus, the meetings work very well with the web version of Microsoft Teams.
As a result, I do not know if it is ESET (ESET Endpoint Security )the problem but in doubt and having seen the question, if you find a solution I'm interested.
Ports 80 and 443 are well open on my side.
in HTTP protocol checking i have 80,8080,3128
Mac Os version : 10.15.4
Version Teams : 1.3.00.8663
Version ESET Endpoint Security: 6.8.400.0
Thank you for your help,