itch.io

I don't remember exactly what the button said, maybe "more"? It's beside the cancel/close button. I pressed that, then when it gave me more information it asked me whether or not I wanted to open the file anyway. That's how you open the game. I'm using windows not a mac but I believe it's the same 

APle moment

Gatekeeper doing its job. You can unlock that in the system preferences under Security. There's a radio button that needs to be checked in order to successfully install third party software that doesn't have. I forget which one off the top of my head but it's under the FileVault tab I think?

Sorry I haven't worked support in a long time and it's escaping me now but I know there's an article about it on the Apple Support website.