This template uses two scripts instead of the standard bootstrap menu for the main menu.
The smartmenus allows the use of drop-down menus on touch devices. This way you can create overview pages as usual. The mmenu side menu is used on small display devices. Here too, you can click on overview pages, but you can also switch between the different levels as you wish.

When structuring the website, you must of course make sure that you do not create too many menu items and possibly "blow up" the design. Depending on the size of the page, the concept has to be changed.