Menuitem appended, how to enable

I appended a submenu item to a file menu but can’t find a way to enable this new menu-item.
FileMenu | Menu1 | Submenu1
How can I enable Submenu1 ?

Add at least one item to the submenu.

Open your window “Window1” => insert => Menu Handler => choose you menu item from the list of menu handler.

This doesn’t apply to this case, since a submenu doesn’t have a menu handler, its children have menu handlers. A submenu is automatically enabled as soon as there is at least one child menu item.