I don't know how Majalis is building the game but I don't think the Mac version has ever worked; it's missing some crucial component to make it run and all the permissions are fucked up, and I've just given up reporting it as an issue.
If you want to play on Mac you need to install Java; the version I'm using is Adopto OpenJDK, which works better than the version from Oracle, you can download that here: https://adoptopenjdk.net
Once you've done that you don't need the Mac application at all, just the .jar file, which you can either download on its own (though it's not always available for every build) or you can extract it from the Mac or Windows app; for the Mac app just right click on the app in the Finder and choose "Show package contents" and the .jar file is in Contents or resources somewhere, just drag it out somewhere you can find it. With OpenJDK installed you should then be able to just double click the .jar file to play.