I figured it out: it was crashing on startup because I was running the linux executable in a temp folder that held an existing options.cfg file (from some other Godot game). When I moved the executable to its own folder, it ran fine and created a fresh options.cfg file in there. I checked with the original build and that also worked once I extracted to its own folder. Sorry to give you a scare (well, it's almost Halloween, I suppose.) Interesting that Godot crashes when it reads an options.cfg file it wasn't expecting.
Ah man, yes you did give me a scare. So glad that you got it sorted though :) I know I should handle checking whether you can write to the folder/the file is valid etc. but I thought I'd wait to handle it until it was a problem ( i.e now).
Thanks for the report and glad you find the games fun, makes it worthwhile!