MacOS has issues selecting the correct working directory. That's why I normally don't make Mac releases.
I actually just dealt with this after going through your platformer tutorial and trying to use PyInstaller to export an executable. There's a function you can find that basically checks the PyInstaller _MEIPASS for the path and then if it's not there grabs the abs path. Then you just throw the assets in the expected dir. It's a bit of a pain because you have to call the function on every single path string you use in the project, but it does fix the problem (when running/exporting exclusively on Mac). Not sure if it would interfere with Windows/Linux stuff.