New to Drupal 8.9 and 9.0 is the ability to create the HTML
element within a native Drupal menu that can be used to toggle secondary menus (such as drop-downs or mega-menus) in a usable and accessible way.
Common inaccessible menu patterns
It’s common to see links (instead of buttons) used to toggle submenus. The result of this pattern is typically inaccessible for keyboard navigation and assistive devices such as screen readers.