Microsoft just released into Targeted Release tenants the ability to add a mega menu navigation at the site collection level.
*If you are looking for a true global navigation solution, you will need to create a custom SharePoint Framework (SPFx) Extension
To change the navigation to the mega menu, click on the site actions menu (gear icon) in the upper right corner of the screen and select “Change the Look” from the dropdown menu.
Select “Navigation” from the menu.
Select “Mega Menu” from the options
To add items to the navigation, select “Edit” from the header navigation.
Add items by clicking on the “+” in between the top navigation items. Select Header for top level items that will not be linked.
Make sure that the Header Item is a sub-link of the top navigation level item.
To add a link below your new header link, click on the “+” and add a link. Select “URL” from the dropdown menu.
The navigation will show from left to right once saved. Make sure that the item link is a sub link of the header item (now the third level down from the top nav item).
Press “save” to save the navigation. Your new mega menu navigation will show as a dropdown from the top-level navigation item.
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