How do I create dropdown menus?
You can add a drop-down menu to your online store's main menu. You can use drop-down menus to group products, collections, or pages together to make it easier for customers to navigate your online store.
To add a drop-down menu from the main menu of your online store:
1. From your Shopify admin, go to Online Store > Navigation.
2. Click the title of your main menu.
3. Choose one of the menu items to be the header for your drop-down menu, or add a new menu item to be the header. If you don't want the header to link to anything, then you can enter
# in the Link field when you add the menu item.
4. Add menu items to include in the new drop-down menu. Click Add menu item, enter the name of the menu item, and enter or select a destination for the link.
5. Click and drag the menu items to nest below the header item:
6. Click Save menu.
Ensure the list handle matches the list name
The most common setup issue happens when the child list handle does not match the parent link text. This can happen when a list is renamed after creation or when a special character like an apostrophe is in the name.
Read the full Shopify article here