1. Make sure the top category has viewable sub-categories. Go to Products & Categories > Browse Categories. Select the main category that has subcategories under it:
2. Now check the box for "List subcategories on Catalog Page". This will list a clickable text list of subcategories underneath the main category. If you have uploaded category images for those subcategories, check the box for "Display subcategory images on Catalog Page?" to show image thumbnails for categories instead of a text list of subcategory names. Then Save your changes.
3. Now go to Cart Settings >> Appearance & Content >> Catalog Settings. Find the setting "Display subcategory products in primary category?" and set to "No", then Save Changes.
This will force customers to click on a subcategory before they can view any products within that subcategory.
