I'm not really a big gamer, but I've made a commitment to run Linux Mint as my DD. I installed Steam today and enabled Proton and gave Shadow of the Tomb Raider a try. I'm running a meager GPU, the RX 560 with less-than-stock RAM clocks, so it wouldn't be the best example of performance. I ran the benchmark at 900p medium, and it managed to pull around 30fps. The only noticable issue I encountered was that there were these vertical beams/tearing that appeared to be coming from Lara's eyes! Not sure what that is all about. I was running AMD-gpu-pro drivers. Not great, but I was impressed with how far Linux gaming has come, as this is not a native game and its a relatively new title.
As for UWP, I hate it. Not sure if it's just UWP, but MS's way of packaging apps is just plain terrible, IMO. Back when I was a devoted MS fan (I had it all--Phone, Band, Surface, Xbox), their app delivery was totally unreliable. There were times when apps refused to even download, much less install, and the troubleshooters did nothing. What I found was that when this happened, you had to delete a random app, and that would fix the installer. UWP seems better, though my most recent attempt to install Forza 7 results in a complete failure to launch, with no error messages whatsoever. I finally just deleted my W10 partition, as I haven't booted into it in weeks. I can always VM a Windows install if I get desperate, but it hasn't happened yet. I'm sure the full-on PC gamer can't do this yet, but I mainly game on a PS4 Pro, mostly for simplicity's sake.