To add product category
to header dropdown, you can follow these.
#1. First, you need to find the product category URL.
You can access the shop page > Click on each category.
then you will see product category URL in browser address bar, something like this
#2. Next, click a Folder Dropdown with the name Shop
#3. Next, under the Shop Folder Dropdown, click Add Page
Choose Link
#4. Enter the Name & URL you have in step #1.
#5. Result