I'm looking for some help regarding nested menus not working on an older theme that my client requested to be imported to their store. Other themes display it correctly.
I think the theme file comes from an older version of Shopify when nested menus were built using handles, therefore it doesn't work with the new menu system. The store link is below:
What should I do?
Yep, that's a theme built when menus were flat. To make drop-downs you had to create another menu with name matching the name of the top level menu item. Say top-menu has "home", "collections","about" and another menu should be called "collections" to create a drop-down.
So you can either do that, or modify the menu code to work with multilevel menus (not that difficult).
However, I expect that this theme would be difficult to configure and very bad in page speed, so I wouldn't put it in production.