We have a new Mac OS X version. Please reply if you're still having issues!
As of 9/14/19 issue has been solved by the link in laikaproj's reply
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Unfortunately, I am still running into the same issue. Just to test it out I've downloaded a couple of other games with mac versions off of Itch , but both of those were able to unzip and open. When I extract the zip there is no indication of anything going wrong during extraction.
Hey! I'm not the dev on the project but I ran into this issue on my own game. The solution should be to change your Mac OS security settings to allow all applications. Unfortunately Apple has hidden this option away pretty heavily so you'll have to go through some steps to enable it: http://osxdaily.com/2016/09/27/allow-apps-from-anywhere-macos-gatekeeper/
That *should* fix it ;)