A bit of an update: I have a suspicion that the code that checks if the app is packaged into an msix package might be causing crashes on Proton (since it doesn't implement the code that is necessary for it). Although I reccomend building a native Linux build, I'll look into better handling this scenario for the bootstrapper.
Thank you for your response. I unfortunately had rather negative experiences in the past on Steam with maintaining both a Linux and a Windows version.
That's why I'm currently only on Windows. If it would be possible to get it running with Proton, that would be amazing. If not, that is of course no problem. :D
Greetings
So... A bit of an update on that side (sort of). I've noticed that the Steam Overlay also didn't work after packing, as the required command line argument wasn't passed to the game's executable. Although I'm not sure if these are correlated, but it's possible that there could be a conflict.
I am working on adding the required flag automatically for the Steam builds, but until then, you can fix that (if needed) by adding the --in-process-gpu in the executable flags (found under Project Settings -> Compiler and Packer -> Halva Settings).