This "Big Test" structure is a copy of the structure at https://link.ssis.edu.vn (test site: https://linktest.ssis.edu.vn) with actual page names replaced, to check how a structure (and menu) of that size works.

I also wanted to check the best location for the menu — top zone or topbar zone — etc. Now the menu at the school site is in the left column but this means it displays (top-level items showing) at the page bottom in mobile view. I think it's better for it to display under the hamburger icon at the page top in mobile view, so we can get this by making it a horizontal menu at the top of the screen.

As for the Smartmenus display and function here, they're great! Thanks to Anton. .