The biggest thing missing for me is good VR support at the OS level. Even with all the optimizations in Bazzite making regular games perform about equivalent to Windows, latency in VR is awful, and motion smoothing just plain isn’t supported in Linux yet, on any hardware. Those two pain points make the experience much worse than on Windows, I’d be motion sick in minutes if I tried to actually play something. Thankfully, normal gaming works just fine, and I don’t play VR as often as flat games, so I can just boot into Windows when I want to do that.
The second thing is the poor state of music players. I’m used to the very extensive feature set in MusicBee, and not a single native player hits all the boxes that MusicBee does. It can be run in Bottles, but not very well, and as a newbie, it took me a lot of extra tinkering to get things working even sort of right - file permissions, dotnet stuff, font libraries, etc. I still haven’t quite gotten file permissions working right, and font rendering is pretty bad (and custom font selection is broken entirely), but maybe I’ll figure some of that out eventually so I can stop booting into Windows whenever I want to make changes to my library.