From Hardlimit
Lots of good games are still not working properly (e.g. Nioh), also modding support is very lacking and cumbersome.
I had some trouble with Nioh, but I remember it working perfectly after trying a few things
That was last year though, I don’t remember what exactly I did to make it work
You can see other people’s issues on ProtonDb https://www.protondb.com/app/485510
Basically no attacking with controller without workaround, movies not playing for some and performance/stability issues.