Alright, so I've tried The Surge and wanted to play it with my Steam Controller.
The game itself is a regular Win32 program, but it's still in that stupid oversecured WindowsApp folder.
Can't add it as a non-Steam game because the application doesn't have permission to open the exe. Hurray.
...You are so close Microsoft, so close! :/
I remembered there is GloSC, so I installed that, but same thing. Ironically GloSC supports UWP games, but that doesn't work either because The Surge is win32
Also I can see how Game Pass makes people buy more games (according to Microsoft). Like, I've tried The Surge now and can see that I'd definitely enjoy that, but it's a long and difficult game and I don't plan to sub to Game Pass forever, so having it in my library and being able to go at it on my own pace will be preferable.
I guess in a sense for some games it's just a glorified paid demo service for me, lol.