Hello,
Those subcategories are hidden because we hide by default categories that don’t have products (there are no reason to search by them because nothing will be found anyway)
Your categories -> https://prnt.sc/GEPOlO92sTyC
Once you will have at least one product for subcategory (to make it not empty) – it will be shown in dropdown -> https://prnt.sc/_qpgy7–bmKw
Testing product -> https://prnt.sc/6GfuxZQAlJtb
Regards