After finally getting everyone online and characters built tonight, we played for way too long before trying to save and ran into a bug which apparently a decent number of people are having. Probably worth just turning off cloud sync for now as we just lost a couple hours of playtime (and learned which person in our group shouldn't be the host and in charge of frequent saving.)
https://www.ign.com/articles/baldurs-gate-3-cant-save-bug
As best as I have been able to figure out, this is a problem with Cross Saves, specifically when you arent signed in to a Larian account.
You can tell right away if there is a problem, as the menu option to save will greyed out with a "game is currently syncing" message.
Happened to me, lost a good few hours of gameplay from last night. I was signed into a Larian account, but with OPs method, it's functional again (though I had to restart because I had no saves from yesterday)