Option to have the grid menu collapsed

Hello,

I have a pretty large menu.

Aesthetically, I love the grid menu, but it would be more functional if 3rd level items could be automatically collapsed when opening 2nd level items (and not have the 2nd level menu re-sorted by which ones lead to a 3rd level menu).

Relatedly, I'd love it if 3rd level options would expand in a grid instead of a vertical list (so that they could fit on smaller tablet screens).

(attached an image of a menu with a similar 3rd-level-grid concept to what I'm suggesting.)

Or alternatively, a way to add/embed a long list of categories into the menu would be great.

Thanks for all the time y'all put into making, maintaining and updating this theme!