Sounds like a genshin problem. Before I had a steam deck, my go to portable emulator was on Android and I even had a little phone holder thing to stick my 8bitdo controller on since all it need was Bluetooth. Not sure about the ultimate controllers, though, as I wasn't a fan of Xbox layouts.
It indeed is. I have many 8bitdo controllers and have no issues with them. It's the fact that genshin would licence out their characters, ignoring the really weird choice of which, for a controller design on an Android compatible controller while still not supporting controller on just android. It would be one of the easiest changes to do out of likely any other code base out there too.