Mega menu can be defined as a drop-down menu with multi-level expansions that shows complete navigation of your website. It helps visitors to reach the deepest section of a website. 

The other thing about mega menus is that it helps enhance the user experience. 

In some cases, it may even appear that the mega menu disappears. One such example is the mega menu is missing when varnish cache is activated in Magento 2.

To get more information, you need to refer the tutorial at:https://meetanshi.com/blog/solved-na...-in-magento-2/