Unfortunately Drupal have no built-in Dropdown menu even a Megamenu. I believe every Drupal Developers use a Dropdown menu rather then click every page to do desire task. Most Developers using Admin Toolbar, Admin Menu, Nice Menu, Superfish, Simple Megamenu, Megamenu, TB Megamenu, OM MAximenu, and so on.
I hope Drupal 8 provides a built in Dropdown menu which support Megamenu, so we can built complex menu using entity.
Closed: won't fix
9.5
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
I personally don't think this is something that core itself should support. As the IS states, there are many contrib modules already that support this. So either one of them or a contrib theme that creates a mega menu should be used.