Hello! Are you running Catalina on your Mac? If so, that’s because Catalina has very strict permissions for unverified apps. There’s a workaround here, although I can’t verify if it actually works because I don’t have a Mac. If you’re running an older OS than Catalina, can you let me know what you’re running and what specifically the error message says and I can try to troubleshoot?
Nope, this was on Mojave. Also that was the exact (and very unhelpful) error message "This app can't be opened". I don't believe this is the usual key signing error you get for unverified apps, because that has a "because the developer couldn't be identified" on the end of the error. This error, which I've had before from itch games, usually means something needs to be set executable, but isn't