There is no native WordPress function that enables menu duplication.
For site owners who desire to duplicate a fairly complex menu, the Duplicate Menu plugin is by far the most efficient option. If you have a smaller menu with 10 or less items, you can manually copy an existing menu without a plugin fairly quickly.
00:00 - Start
00:16 - Manual menu duplication
01:13 - Automated menu duplication with the 'Duplicate Menu' plugin
Full blog post: https://nichetwins.com/wordpress-duplicate-menu/
