It's been a few months since I played but the only thing that doesn't work is Xbox login. I needed to download a DLL to get multiplayer working, which I agree isn't really userfriendly, but compared to the early Wine days Proton is a walk in the park.

What I do miss a bit is Capturage, apparently it's really hard to make it work in Proton.

It's even been less troublesome than when I used to use AMD GPUs, where IIRC accelerated graphics drivers and the ROCm drivers had some sort of conflict unless installed a certain way (a few years ago now, my last AMD card was a 5700xt).

The only problems I’ve had are that the intro video and menu for supreme commander forged alliance runs at very low frame rate (but the actual game runs without problems), and that Gothic 3 was very glitchy on steam deck. Everything else I’ve tried ran without issue.

No idea where that came from but it's not the case.