We are aware of reports that the mouse cursor isn't functioning in the Mac App Store version of SimCity Complete. This issue has been flagged with our team and our investigation is underway.
In the meantime, we do have a workaround so that you get back to playing.
Activate Windowed Mode to Resolve this Issue
Click on the Settings icon in the SimCity Launcher and then select "Play in Window" and the game will launch without issue. You can then adjust the resolution settings from the Main Menu in order to resize this window.
Having trouble? Check out the image below: