Couldn't get the Mac OS version to run on Big Sur 11.3.1. I get a You do not have permission to open the application “CaveSlime” dialog when I attempt to launch. Didn't solve it with moderate amount of googling.
Thanks for the comment! I just updated the itch.io download popup to explain how to fix this. Alternatively, if you haven't already, you can download the official itch.io app and it will automatically work without running any commands.