I've been on linux for 4ish years, and I've done a fair share of gaming in that time, with minimal issues

The few I can think of are mostly controller related:

• having downloaded steam as a flatpak originally I ran into some issues with missing inputs in the steam input software (getting the .deb version of steam fixed it)
• warframe crashes when switching windows with a controller connected
• running steam in big picture mode results in some keyboard keys not working in certain games (o is the one I remember but there were a few of them)

Oh and one other I had was initially getting sims 3 running, but that one was fixed at some point and now it runs fine