From Xojo Documentation
Used to handle the application’s and windows’ menu bar.
When you create a new desktop project, a default MenuBar (called MainMenuBar) is added to your project.
You can refer to a MenuBar globally by its name because an "implicit instance" is automatically created for you to use. If you use the global name, then you will get the same MenuBar instance everywhere you use it. If you modify the MenuBar in code, the modification will appear everywhere the MenuBar is used.
If you would rather have separate instances of the MenuBar, you should assign it in code manually in the Window.Open event:
See examples for the MenuItem class.