How to add icons and images to the menu
Since 6.9.1 theme update, the following plugins can be used to add images, icons and SVG icons to the menu items.
https://wordpress.org/plugins/menu-image/ (allow to add only images) or https://wordpress.org/plugins/menu-icons/ For more details, please refer to the plugins documentation.
You can also try using The7 MegaMenu feature.