These are top and recommended Mega Menu Extension For Magento Ecommerce:

1. Landofcoder Mega Menu PRO Extension: This Magento 2 Mega Menu PRO extension helps you to create dynamic navigation menu ever with powerful features:
+ Drag & Drop Intuitive Interface
+ Import Categories to Menu Instantly
+ Fastest Load Time, Cache Supported
+ User-friendly Interface & Enhanced UX / UI
+ Fast Ajax Load & Live Preview
+ Skin Builder: Custom Design With Ease
+ 16 Premade Menus & Create Unlimited Menu Possibilities
...

2. Rootway Mega Menu Extension for Magento 2

Rootways Mega Menu is a Magento 2 extension, and it is your easy and fast solution to create the best sitemap right on the main navigation of your Magento 2 website.

- Create mega menu by just selecting mega menu types.
- Manage design from admin.
- Set number of columns.
- Set content at top, bottom, left and right.
- Category icon and label.
- Automatic height adjustment.
- Custom links to mega menu
Link: https://www.rootways.com/shop/magento-2-mega-menu-extension

3. Magedelight Mega Menu Extension for Magento 2: This Magento 2 mega menu extension helps to create dynamic navigation mega menu and display anywhere in Magento store to provide a fast and flexible way to access different pages across the website

Link: https://www.magedelight.com/mega-menu-magento-2.html

4. Magesolution Mega Menu PRO Extension: Magento Mega Menu changes the way main menu displays. It allows you to have multiple options to show what you want on the main navigation

Link: https://www.magesolution.com/mgs-mega-menu.html