It would be great if ACF supports adding custom metaboxes with menu items to WP Nav Menus.
For example, when somebody installs Polylang plugin and go to menu page, it seems something like this:

https://imgur.com/a/sjWj7Qb
On the left, you have “Language Switcher” block and can select “language switcher” to be added to the menu. Next in the “language switcher” menu item there are some options – Display as dropdown, Display as flags, etc. I guess it is not top-priority, but in my opinion if more people see this feature exist will want it.
ACF has the ability to add fields to menus and menu items