This help page explains how to use Maple in full screen mode on Mac.

To expand to full screen:

Under the View menu, select Full Screen Mode.

To leave full screen mode and return to the standard view:

Hover your mouse over the top of the window to view the Standard Menu Bar.  Under the View menu, clear the check box for Full Screen Mode.

Alternatively, use the key combination Control + Command + F to toggle full screen mode.