In my experience, not great. I have a 1080ti and run 2k ultrawide. A bit dated but still a pretty powerful card. Some games weren't too noticably different but on cyberpunk for instance I took a huge performance hit and had to adjust my game to look basically terrible to get it playable compared to windows. I think I did this by setting superfx to performance.
I have to say though, I am running a pretty old processor (barely meets win11 spec) so that could be contributing to my issues.
For most games I'm sure you can find a way to do it. If you use protontricks you are able to run an exe under a proton prefix for a game (basically a virtual windows drive in a folder for the game) which I've had pretty decent luck with.
If you play games that support mod organizer 2, there is a sh install script somewhere for support in proton/steam that works well (I can find if you like), but the program does run pretty slow and is fairly buggy. Usable with patience. Upside is it can run MO2 for a given game direct from steam if configured correctly