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 "Shop by Pet" menu item:
vamtam-menu-click-on-hover mega-menu-home-mix
Tip: If you don't see the CSS Classes field, ensure it's enabled in the Screen Options:
STEP 2: How to edit the "Shop by Pet" popup mega menu?
The "Shop by Pet" navigation item leads to the "Mega menu - Home Mix" 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 "Shop by Pet" mega menu is to mouse over the "Edit with Elementor" link and click on the "Mega menu - Home Mix" popup:
Trying to edit the "Mega menu - Home Mix" popup with Elementor, you'll notice that it's a Tabs element, and each tab contains an Elementor template:
The easiest way to access these templates is to mouse-hover the "Edit with Elementor" link on the top Toolbar and locate the tabs' templates:
Clicking on each of them will redirect you to the template's content. Here, you can select the post category for each tab. Make your customizations following this guide: Guide to Vamtam Elementor Builder
You can also access the templates from Dashboard > Templates > Saved Templates:
Please check these guides for further information:
https://elementor.com/help/elementors-theme-builder/