Unfortunately, I'm not a Mac user so I can only pass along information second-hand that may be able to help you. You may be able to right-click the icon and choose "Show Package Contents", and then go into the folders to find a different launcher that should? work.
In this case, I went into the Obscura.app folder, then Contents, and then MacOS, and there was a file called Obscura there, which hopefully launch the game? I'm afraid I can only be of so much help in this case; this is a tutorial from a dev friend of ours who has been able to use this method before, but I can't test it on my own.