Hello,
You have built the mega menu in the wrong way, you don’t need to define subitems via Appearance -> Menus, as you have now: https://prnt.sc/1yIAoVe_iRkX
Remove these subitems and just define the HTML block with the menu to the appropriate menu item in the “HTML block for dropdown list” field: https://prnt.sc/PfMd9zJNK-bH
So as a result, that HTML block with the menu will be as a mega menu.
https://xtemos.com/docs-topic/create-mega-menu/
You can also reach out to us if you have any questions.
Kind Regards