Well, it completely breaks the resolution selector in the game properties. I think ideally the deck should still have it all functioning if it is possible to check the hardware, but I'm not sure if gamescope even supports anything like that.
I generally play my games at 720 with fsr on deck, unless I am confident that the deck can handle it. Sure I could just change the resolution in the games settings, but sometimes there are some games or applications that I just don't want to deal with and gamescope just handles it. It's not a huge deal, but that explains why the resolution option didn't do anything for me lately