Since I started this whole project and was able to fully use my gaming guest, I played quite some games. Most games worked out of the box as if I played on a bare metal installation. None of them crashed just because I played within a virtual machine and I couldn't recognize any difference from playing games on a native Windows build. It is safe to say that you can play nearly all of your games perfectly fine within a guest that uses a dedicated GPU. Only a few games will not run on such a machine. I listed them down below in the exceptions section.
I tested Rage 2 on the first Windows VM that I created and had no issues at all. At some parts of the game, I noticed some weird flickering but I don't know what caused it. Either it is a bug of the game, it was meant as a feature (the locations and scenes would have matched to that flickering) or it is because of my VM. Either way, I'm really happy about the result and can't complain about the performance. More detailed tests are already planned and will be added to this section as well.
Overwatch was the second game I tested. Compared to Rage 2 it's not a big deal for mid to high-end machines. Getting constant 60fps should not be a problem for most modern machines but since I'm using a 144Hz monitor for all of my games, I needed to reach those 144fps. Everything I can say so far is that Overwatch runs flawlessly as well. The virtual machine has enough power to run the game at constant 144fps and I didn't run into any problem or the previously mentioned flickering or somehting similar. Apart from Overwatch being the game I played mostly at that time, I chose it because I've never heard of any problems with its anti-cheat software. It also runs under Linux if you're using Proton, therefore I had no worries about getting banned, kicked or whatever.
Recently I started playing Chivalry 2 and I really enjoyed playing it within my Windows guest. I didn't experience any bugs or crashes and had a similar performance to my native build. I was also able to use my host keyboard because of Barrier. But be aware, you can't use your host mouse unless you want to play with very weird mouse movements. It only happened to me when I was playing a game in fullscreen mode but I'm fine with using another mouse for games as long as I'm able to use only one mouse for desktop stuff on guest and host.
Valorant does not run within a Windows guest, at least not without trying to surpass their anticheat called "Vanguard". Vanguard needs to be loaded at boot time and can't be initialized in a virtual machine. Some people were able to play Valorant but only by modifying their guests in a very specific way which also lead to bans in some cases. For about one week in April in 2021, there was a workaround that worked flawlessly. You were able to play Valorant respectively load Vanguard. Cheating wasn't simplified by this technique, nonetheless Riot Games decided to introduce a patch that kinda killed the workaround. If you want to know more about it, watch this video.
Escape From Takov or in short "EFT" uses BattlEye as its anticheat. In mid 2020 an update was released which probably lead to a better VM detection of BattlEye for EFT. As a result , many players using a KVM for playing EFT weren't able to join a server anymore. Since then EFT is one of the games which cannot be played within a virtual machine.
For resons of simplification I'll call the game Tom Clancy's Rainbow Six Siege only "Rainbow Six". So Rainbow Six also uses BattlEye and can't be played within a VM for a similar reason. Of course, there are some workarounds to hide anything that reveals the virtual machine. By the way, the same workaround which worked for Valorant for about one week also worked for Rainbow Six. In this case it seems to be a bit easier to run Rainbow Six in a VM nowadays but be careful when trying so, you always risk a game ban.
Another game that won't run that easy within a virtual machine is Genshin Impact. The current workaround doesn't seem to be very difficult but you have to adjust your guest configuration in order to play the game. Some workarounds can be found in this Reddit thread.