Screensharing laggy AF / iMac 27 inch (2020)

Hi, I am on a maxed out 27 inch iMac from 2020. Not new but decent machine still imho. 

- 3,8 GHz 8-Core Intel Core i7

- AMD Radeon Pro 5700 XT 16 GB

- 128 GB 2667 MHz DDR4

In 2024 before updating to Sonoma Zoom worked fine. No lag in video or screensharing.
For months now Zoom just lags constantly and slows down machine even after call has ended. why?

- I have tried to downgrade Zoom. no success
- even got me faster internet, using lan cable. no success
- limiting frames when sharing. no success

Google Meet works fine, even Teams without issues. Why the heck is Zoom such a problem?
Anyone got any ideas, tricks, tips? Thank you