Hello ! On my side, I managed to execute the game using "chmod +x ProjectHollow.exe" then "./ProjectHollow.exe" in a terminal. Sorry, I don't know how steam proton work but I hope this still helps.
Hello, the file that’s supplied (ProjectHollow.exe) is a Windows binary. How are you running that file like that? It doesn’t work on Linux because it’s a Windows executable file. Since you are using Unity, you would need to export the project to Linux and provide that as a separate upload. Same for mac - mac users won’t be able to use ProjectHollow.exe either.