In this post, we'll show you how to add icon to menu item in Ninja Menus, a simple but powerful Magento 2 mega menu extension.
https://www.magezon.com/magento-2-mega-menu.html

1. In the menu edit page, open the menu builder section. Then hover over the menu item you want to add icon and click Edit in the drop-down menu to open the settings.

2. Open Icon tab, then turn on Show Icon button.
- Position: set the icon's position to be on the Left or Right of the menu item.
- Icon / Icon on Hover: choose the main icon and the icon on hover from 2 libraries: Awesome 5 and Open Iconic.
- Icon Color: choose color for the icon.
- Custom Class: add additional custom class to customize the icon further.
Remember to click Save after finishing.