Hello,

Create an HTML block using Extra menu list element. Make all your subcategories in a way like this: https://gyazo.com/75153b3d92de0cc21e3f4a59e25e710f and add to the menu.

Instructions for HTML blocks are here https://xtemos.com/docs/woodmart/html-blocks-2/

And here are the instructions for Mega menu https://xtemos.com/docs/woodmart/create-menu-2/

Best Regards