Thanks for the quick reply! I'm on OS Catalina. I'm not sure if it would work in this particular case but I had a previous experience where a game launched sucessfully through Steam even though the direct file on Itch.io didn't work.
Aha. I'll ask a friend of mine who has a Mac to try out the file and see if it works. The Steam library only has a Windows version at this time, since Apple needs to test the product before they allow the game to be available. I hope I can get the Mac version on there for December though, so I'll be sure to message you a key.