It is possible to have many pages and folders in the menu, but the amount visible is limited by the width of the device used.
So the amount of pages/folders visible in the menu on a mobile device is fewer than when using a computer or larger tablet.
The rest of the menu items are neatly stacked under the three lines (also called the hamburger menu) on the right side of the name menu.
Mobile menu opened:
Laptop menu for comparison:
If there is a need to have more pages/folders visible without stacking, use shorter page and folder names.