Apologies, I thought I had replied to this when it was posted. At the time, I had no Mac available to test on, and had no clue why it would've stopped working as I hadn't changed anything. So I didn't even know what version did work.
Turns out - it's nothing I did. Apple just altered their old "this file doesn't have a certificate and may be dangerous, do you want to run it anyway" message to "this file is damaged, do you want us to delete it?" The only way anyone has found to resolve this is to:
- Have me buy a Mac and a dev license for $100/year, which isn't going to happen.
- Manually run a script to disable the certificate check before running the game.
- Possibly running the Steam version might let it use Steam's certificate.
When the next version is out, the Mac download will include instructions on how to disable the certificate check for those who want to.