Bought the game and am loving playing it on the steam deck. Only weirdness I've seen so far is that when I favorite title.p8 in splore, the title of the game just reads "title" instead of Astra and the New Constellation. It's purely cosmetic, I realize, but consider renaming title.p8 to the game's title and updating the level p8 files accordingly?
Otherwise, my only frustration so far is relationship between stomp dropping and springs. Specifically, hitting stomp in the air when hitting a spring for the first time should result in an immediate high jump, but instead I have to land on the spring first and then immediately stomp which sometimes/often mutes the height I get the first time. I find that it messes with the flow and has caused a ton of extra deaths.