I got it to work, so it seems that your Linux build for whatever reason does not have execute permissions. (I've encounted this with a few other Godot games) In any unix environment (Windows Linux subsystem would work), you can run `sudo chmod +x APPFILE.x86_64` and that'll fix the issue.
Btw, good game, it played pretty well. I stood on the sides of the walls a few times, but I'm not sure if that was intentional or not. lol