Hey, sorry you're having trouble running the game.
Unfortunately, if the problem is not addressed in the readme file included with the OS version specifically, it is probably beyond my ability to fix: Mac OS has become more and more hostile to Unity games over the years, especially games made in older versions of Unity. In truth, I have not had a Mac capable of running Demon for a few years now, but up until this point the readme has been able to resolve issues, so I hope it works for you.
If you already tried it and/or it doesn't work, I'm afraid I can only offer my apologies.