Hey Raiders!
I've added Steam Deck compatibility in the latest r967 update via some initial input mapping in the Unity Input Manager, and added a Gamepad submenu to the Options menu listing the default controls.
You might want to lower the sensitivity of the right joystick in your Steam Deck for aiming purposes. Go to Controller Settings (in the Game Launcher) > Edit Layout > Joysticks > Right/Left Joystick Behavior Setting symbol.
Hope you enjoy!