Hi Massimiliano,
It's all about content that you will publish in MegaMenu, example from Investa (joomshaper)
as you can see there, it was and is possible to use any module inside MegeMenu as submenu items.
Also with icons, images or video clips.
Probably YooTheme made that same in that submenu. They used a module(s).
In that guide: https://www.joomshaper.com/documentation/helix-framework/menu-navigation
Find section "How to add a module inside the submenu" (in the middle)
Of course first create a module(s) with text and icons. It can be SPPB module as well.
A module can display "dynamic" content as well, current news or custom code, anything you can create/develop. It's on your hands now!