Nvidia. Installed System Shock 2 (through Steam) on my Linux machine at work. Ran it, cool, left the game and resolution was stuck at a really weird one (on 1 of 2 monitors) and I had to fix a problem.
Same game on Windows, likely no problem to fix.
Issues for sure still happen with Linux gaming. Many games are fine though, of course.
I have a dual screen desktop running Arch and I play games a lot, on the radeonSI Gallium driver and Intel driver.
The funny thing with multi-screen gaming on Linux is that the "default" target SDL picks is not your primary monitor, it is the monitor on the left. It doesn't matter what input order its in, or anything else, I can reconfigure my screens however I want but "full screen" always means leftmost panel.
No issues here. I guess you may be running AMD hardware hence the video drivers issues, but I haven't had sound issues in games for years.