I ran into the issue of not being able to load savegames. Twenty hours in (for the second time - the first time I lost it because I was playing on Stadia but they shut the service down!)

Here is how I fixed it:

Launch Steam
Right click BG3, choose Properties
Click on Betas
Click the dropdown and choose the latest beta option (mine was 8 at the time)
exit out, wait for the game to update (42GB download for me)
Once I launched the game again, I was good to go - all my savegames were available