I had a bunch of fun with this! Took me a little while to notice that mouselook was an option, but once I did, I was able to find all of the gems and coins. Nice work!
Hope you had a positive experience using Godot, and thanks for doing Linux builds. Always nice to see source code too! :)
Regarding Mac builds being "damaged" when exported from non-Mac operating systems, the issue is with app signing and "quarantine" flags that are automatically applied to downloaded applications. If users install and run the game via the Itch app, that'll get them up and running with unsigned builds.