The Linux version (and it looks like the Windows version too) are just the Godot binary, and are missing the .pck file that has the actual game data. It looks like the MacOS zip has the .pck, so I was able to play by combining the .pck from the MacOS zip with the Linux binary.
I like that you had voice acting and a narrative mission structure. I enjoyed the PS1 style. The switch to FPS combat was fun. It would be nice if the text was larger for my old man eyes. :-) Also, on my first play through the baddies spawn right on me and I immediately died, and didn't really know what was happening. Finished on the 2nd play through.
Congrats on finishing! Every game is a miracle. :-)