At first I launched the game just after it finished installing and had this issue where the mouse cursor kept getting stuck which basically made the game unplayable. As it turns out, somehow the game was still missing an update after the fresh install, it downloaded after I closed the game and then worked fine afterwards. If you experience the same issue, make sure you see the "Henteko Doujin" logo at startup, if you don't see it, you're not running the latest version.
Other than that, I didn't notice any problems. The game was designed with kb&m controls in mind so aiming with a controller is very awkward, but it works really well on the Deck if you use the right trackpad for mouse input.
Plays fine but with minor frame pacing issues and occasional freezing
Game loses focus and freezes when the reticle goes outside the window
Both native and Proton will freeze occasionally when firing while the reticle is at the edge of the screen, causing the game to lose focus. Can be unfrozen by tapping in bounds.
Both native and Proton have slight scrolling stutter due to poor frame pacing. Set refresh rate to 58 Hz or cap FPS to 58 to get smoother performance.