Trying to see if I can help. Could you explain in a different way what you are trying to accomplish? There are a number of topics in this forum that deal with creating sub-menus items you can find with a search.
Or are you just talking about making a group inside a group inside another group? You can show and hide things using the “on hover” conditional; so that would give you a clue on how to create your own.
Create a group, expand it. Make it blue. Call it menu.
Make a group inside the blue group. Make it purple. Expand it but still smaller that the blue group.
Inside the the purple group create a link element, smaller than the group.
Alternatively:
Then problem is that when you right click on an element and select Group Element… It makes a group exactly the size of the element itself. So it’s hard to see what you did. Grab the expanding “ears” to expand it and see the new group.
I have the very same problem. For some reason, an element on my index was left behind when group A was being created. Now I want to see if I can make that element a Group A"child".