itch.io

You should be able to use it even though it can't be verified, I would search google for the how to for all that.  If not you can always use a virtual computer program and run it as windows or linux that should bypass the macOS and allow you to play games outside of it.  Hope you find a solution, its a pretty awesome game.

It's the same with every AVN on a mac, have you not played any before?

when you get that warning, click Cancel. open System Settings, go to Privacy & Security, scroll down to where it mentions The Headmaster, click Open Anyway. Use Password, then Open.