Even with all graphics at the lowest settings, the game can barely maintain 60 FPS at the Deck's native resolution. You'll either want to cap at 30 FPS (which IMO isn't ideal for this type of game, or drop the resolution to 960x600 as well as lower graphics setting down one step from their defaults.

Unfortunately, the Linux version of the game doesn't list 960x600 as an option, only 960x540, and choosing the latter results in improper scaling - the game image is squished horizontally. So to get proper scaling at lower resolutions you'll have to switch to Proton.