I don’t know where the default working directory is when double clicking the App Bundle, maybe somewhere not writable?
Yep, that will be the case. It maybe sandboxes the game or something. Godot's API will just silently fail and carry on.
...Godot also suggests using that directory via the user:// prefix to keep the behavior portable.Indeed I am well aware, but when developing it is much easier and portable if it's in the directory where it runs. Being able to simply dump the application directory which also holds it's persistent data is simpler than sifting through to find the hidden directories.
I'll do another quick release with the mac version saving to the user directory.