STEP 1: How to trigger a Popup from a Nav menu item?
You can have a mega menu type of navigation using the Popup Elementor feature. Please check the detailed tutorial below:
https://elementor.com/help/how-to-trigger-a-popup-from-a-nav-menu-item/
This is the CSS class added to the "Services" menu item:
mega-menu-services-big-construction
Tip: If you don't see the CSS Classes field, ensure it's enabled in the Screen Options:
STEP 2: How to edit the Services popup mega menu?
The "Services" navigation item leads to the "Mega Menu - Services" popup. You can locate this template in Dashboard > Templates > Popups.
Click on "Edit with Elementor" to edit the menu, images, button's link, etc.
Read more about the Elementor Popups
https://elementor.com/help/how-do-i-create-my-first-popup/
Another way to quickly access the Services mega menu is to mouse over the "Edit with Elementor" link and click on the "Mega Menu - Services" popup:
Please check these guides for further information:
https://elementor.com/help/elementors-theme-builder/
Follow the above steps for customizing the "About Us" and "Work" menus.