I don't think it is a problem with the certification. Most games released on Itch.io and gamejolt aren't from identified developers and to play them, you either need to disable Security and Privacy settings or go to the Security and Privacy settings and basically say that it's okay for that specific game to run. The problem is when I go to play it, it says that it is damaged and should be moved to the trash. I've had this happen with a few different downloaded games, but I don't know why it happens.
Still, I appreciate you trying to make it work. Good luck with your future projects.