The Full Screen mode of Atlantis is fully customizable. On the View tab of the "Tools | Options..." dialog, you can specify which components of the Atlantis window will be displayed under the Full Screen mode:
By default, the main menu is not available under the Full Screen mode. But this main menu will appear if you ride your mouse against the top edge of the screen, and click:
When one menu item is visible, dragging the mouse cursor right or left along the top edge of the screen will display the other menu items.
See also...