With the new version the launcher won't launch the game in it's current state.

Fix by:

Right clicking "Launcher.app" and choosing show package contents.
open "info.plist" in the "Contents" folder
edit the "GamePath" line from "./Amnesia.app/Contents/MacOS/AmnesiaSteam" to "./Amnesia.app/Contents/MacOS/Amnesia" (I.E. delete the word Steam) and save

It should now work when you click "Launch game" or "Justine"