I have no experience with that specific game, but I connect my Steam Deck quite regularly to a 4k monitor, but running that in 1080p. Some games might depend more on the CPU and can take the bump up from 800p to 1080p just fine. I suggest you playing on the monitor you like the color/brightness the most, regardless of native resolution, locking the framerate at 30Hz and enabling FSR on the side menu. Try 1080p and if you notice a performance issue, go back to 720p.