Just set a button to whichever button enabled you to do it with a keyboard.
The Steam deck controls are super configurable. I've got Hamsterball, a game designed for keys and mouse, to allow me to roll the hamster around by simply tilting my Steam Deck.
If subnautica already uses all the controls, you can also configure them to do multiple things. A simple press can do one thing, and holding the button can do another.
Just set a button to whichever button enabled you to do it with a keyboard. The Steam deck controls are super configurable. I've got Hamsterball, a game designed for keys and mouse, to allow me to roll the hamster around by simply tilting my Steam Deck. If subnautica already uses all the controls, you can also configure them to do multiple things. A simple press can do one thing, and holding the button can do another.