Sketchup 2021 freezes every time at quitting on iMac 2020

Hi,
on my new iMac, every time I want to quit SU, the ball of death appears. I tried everything, a new installation, erasing the json files in application support. Erasing all plugins.

Any ideas?

Frank

iMac (Retina 5K, 27", 2020) | 3,8 GHz 8-Core Intel Core i7 | 128 GB 2667 MHz DDR4 | AMD Radeon Pro 5700 XT 16 GB | SU Pro 21.0.392