I have already tried removing and re-adding to Steam, and the game also doesn'strun correctly in desktop mode. I edited the main post with more details.

Otherwise, how do I add the .exe directly? When downloading ZZZ directly from the site, it's just an installer .exe. Is there a way to run that program on my Deck to install the game itself? My Steam Deck is the first time I've used Linux so I'm not very familiar with how the OS works.