The current input setup for the Steam Deck is, most part, functional.
As it stands, however, some manual rejigging is necessary.
The good news is that more generally, very little else needs changing in pursuit of ideal Steam Decking.

Except, um, the bounced light approximation toggle, which is currently bugged into self-reverting to Ultra.
Basically, anything you might hold while your right thumb spins the camera around.