Does it work on Proton? if it's a Ren'Py game, it might work if you follow the porting instructions as if you made the game.
Viewing post in Hayven Celestia: Under One Sky comments
Oh no it’s not made with Ren’Py, I’m familiar with that and I wouldn’t have had isseues had that been the case. It’s made in godot, which I know nothing about using, and since I can’t use emulation either on here I’m kinda out of options I know about
I just hope they could make a linux version, considering godot is FOSS there’s a chance it might be super easy for them and they simply overlooked the option
Since the potential playerbase on linux that can’t/won’t simply emulate it instead is probably super tiny it’s probably the only way it’d be worth the effort on their part