Hi there! Have you tried installing using the itch app? https://itch.io/app
This app should help keep things up to date and make sure the application can run properly. I just tested downloading using it and it seemed to work.
An alternative to try: Sometimes Mac security controls will stop apps that it doesn't recognize from running. You can try holding the control key and selecting open from the menu. This should give you an option to open the application directly.
I hope one of these solutions resolves the problem for you!