The Menu UI component doesn't use the Primitive/Variant system. Instead it uses two prefabs combined. 
Menu structure in Unity
Menu prefabs
Sidebar Menu
Menu Sidebar OnPanel
Menu Sidebar OffPanel
Menu Sidebar Item
Horizontal Menu
Menu Horizontal Item
Menu Horizontal OffPanel
Menu Horizontal OnPanel
Find them in 
FloatGrids/Design System/UI Components/Menu/Horizontal Menu
FloatGrids/Design System/UI Components/Menu/SidebarMenu

Last modified 3mo ago