Genshin Impact

This actually works flawlessly, you just need to add the Hoyo launcher to Steam and set certain Proton environment variables. I'll put info on here later, but it only took me a couple of tries to get it working.

I can't recall if I added the Hoyo launcher that I already had on my external SSD, or if I downloaded it from their website and installed a fresh copy.

Either way, once the Hoyo launcher is running, point it to your existing Genshin game files location.

So far, I've had no problems with it, including updates, both outside and inside the game.