For now, please try right-clicking the unzipped .app file and selecting Open.
When macOS prompts you, click Open again.
Let me know how it goes.
I figured out what the problem is, and unfortunately it is not fixable. This does not mean you can't play the game on Mac. You can try downloading the Windows version and using a tool like Whiskey to emulate it. For more info head over to the downloads and watch the video linked in the Mac install instructions.
Or just watch it here: