Here, Have a Closer Look at it
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Gantry 5 features an advanced and user friendly Menu Editor, which augments the core menu with a rich, drag and drop enhanced interface, to easily change the menu's frontend appearance, such as columns.
The Menu Editor panel takes what your CMS' built-in Menu Manager has and enables you to override it. Changes you make in this panel do not in any way affect the way the CMS handles Menu items.