An unknown bug has been preventing play on most Mac systems. It is unknown how long this bug has been affecting game launch, but it has been resolved as of today.
Follow these steps to restore functionality to the game
1: Launch Steam
2. Right click on Cross of Auria
3. Select Properties
4. In the properties window, select the Betas tab.
5. In the betas drop down box, select the one titled "Mac".
This is an unfinished version of the 2.4.5 patch that will be released in the next few weeks.
At the release of 2.4.5 for windows, this "mac" Beta will be removed and all Mac users will automatically be brought to the functional version of the game.
Note to Windows/Linux users: Opting into the "Mac" beta will not allow access to 2.4.5, as the files are only packed into the Game.App and not the www folder. Release will be soon :)