I extracted the game using the built in Archive Utility. There isn't an option to enable unregistered developers, however, there is an option to allows apps "From App Store and identified developers", which I already have ticked.
To open an app from an unidentified dev, you have to go to Security and Preferences and press allow anyway for the app. I've already done this- but the app still won't open. I've also tried restarting the laptop- no change still.