It causes a bunch of weird controller errors, such as when a controller disconnects (or if the deck goes to sleep), it can’t reconnect again.
Just let it use the default version (which I believe should be Proton Hotfix, or whatever Valve decides it should be since BG3 is an AAA headliner, they’ll want this to work)
That’s normal, I have been using fsr from steam deck’s menu and got it running at 30 fps for the most part, it can still go below 30 but it is very playable.