I'm playing on a Steam Deck, launching through ProtonTricks Launcher. Generally the only time I see performance issues like this is with indie Unreal games.
Regarding the controls, as I mentioned the camera controls didn't work at first and just randomly started working after encountering the first enemy. Camera sensitivity was a bit too high for me as well. Whenever possible, you should have things like that be adjustable.
I recall the combat controls used some of the same buttons as non-combat, W and E. So imagine I wanted to map those to a gamepad, those same redundancies would be present there.