People - I found the bug and some kind of a solution with the help of seo-praxis.de
Main question: If you are joining a teams meeting, your pc is getting very loud, and slow?
Question 1: Do you use Teams MacOS App?
Question 2: Do you use external screens?
Then the solution might be working for you as well.
Step 1: Go into an empty meeting/test with a friend & close all other Apps beside Teams.
Step 2: Open "Activity Monitor" and watch CPU usage.
Step 3: Wait until the mac CPU usage is getting high (>50%)
Step 4: Don't get angry.
Step 5: Disconnect all external monitors.
Step 6: Wait 1-3minutes (it sometimes takes a while).
Step 7: Your mac should now be down to <20% CPU usage and you can have the meeting normally.
Since the Team around Teams is obviously not able to fix this bug since 2 years..
at least the solution will enable you to take part in meetings again.
Thanks goes to Technical SEO Agency from Freiburg Breisgau seo-praxis.de