In order to enable the quit menu item within the application menu, the menu bar needs to have a menu item under the File menu with a standard action "Quit". This was done to follow the Apple User Interface (UI) guidelines.
Here is a screenshot of when the menu item has the associated standard action Quit applied:
Here is a screenshot of when the menu item does not have the associated standard action Quit applied:
With the standard action of Quit, 4D automatically enables the "Quit" item under the application menu. Note that the name of the menu item assigned to Quit is not relevant.