aha! looks like the problem is because (at least some flavours of?) linux don't like running executables directly from a GUI/file explorer window - you're meant to have a special .desktop metadata file, or a shell script.. i've updated it (grab POTION_linux_v2b.zip) with some shell scripts in there ("run_windowed", "run_fullscreen") which simply load the executable - hopefully these will make it work! seems to do the trick here. sorry about that, i just run things from commandline so didn't notice this was a thing.. please let me know if you try it and still no luck.
(the thing i thought i might've forgotten was to link it to the included copy of the GLEW lib - had this problem in the past, not all linux distros have this lib in their repos apparently. but nah, i'd remembered it this time, phew)