Working with WordPress menus, I wanted a top-level navigation element to act as a trigger for a drop-down menu.
It took me some time to figure out how to make this navigation element not redirect anywhere, but it was so easy.
You need to take the following steps:
Insert a custom link with any link address and label that you want.
Click on the 'Edit Menu Item' and delete the link that you insert previously.
Create the sub-menu with the wanted links.
That's all, nothing more, nothing less.