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)
I have this problem with Skyrim and Fallout 4 if I use an external controller (either USB or Bluetooth) when docked. If the controller gets disconnected or I touch any of the Deck’s own controls when playing, the game will just completely stop listening to the external controller and will only work if I use the Deck’s controls. Restarting the game does fix it but it’s pretty annoying, and eg. toggling steam input off and on doesn’t do anything and the controller order is correct.