[2022] CK3 crashes when saving to cloud on Steam/MacOS

Please try a Steam Flush config:

Steam Support :: Clear download cache

support.steampowered.com
If that doesn't help, a clean reinstall of Steam:

Steam Support :: Removing and Reinstalling Steam on a Mac

support.steampowered.com
Good luck!  

The game was updated to 1.6.1 a couple of days ago, then 1.6.1.1 last night. I would have thought saves from 1.6 or 1.6.0.1 would still work though, despite that warning.