Putting a “#” on a menu link which isn’t supposed to be a link is a standard practice and I would suggest that you retain that. Moreover the menu is dynamically generated so you cannot edit it easily.
What we can do is apply a css so that the mouse pointer changes so that it doesn’t look clickable. You need to apply a class called nonclickable to the top menu items. You may need to enable “CSS Classes” in the “Screen Options” visible at the top right on admin section for the option to appear. After that you need to add the following style in custom css.
.nonclickable ul a