Woocommerce "Related Products", how to show subcategory and not parent category

Hi there everyone

I have product detail pages set up on my development site, and at the bottom use a “related products” element with the intention to show up to 4 products from the same sub-category of the focus product. this works ok if the Parent Category only has 1 sub-category.

However, if I have a Parent category with several other sub-categories, I run into difficulty with what is displayed.
Example:
Parent Category: Libeluile (brand)
Sub Category 1: Gourmet Oils
Sub Category 2: Gourmet Vinegars
Sub Category 3: Gift Boxes

If I have a Product detail page from Gourmet Vinegars, I want the “related products” element to only show up to 4 other Gourmet Vinegars from that range. But, unfortunately this element is currently displaying Gourmet Vinegars but also products from the other 2 sub categories of Gourmet Oils and Gift Boxes. I am guessing because it refers to the Parent category for selection.

Is there a way to tweak the settings/code so that the related products element on these pages only displays products from that same subcategory rather than all of them from the parent category?

I did think I could use Linked Products/Upsells when creating the product, and then specify 4 from the same sub category, and then specify “Upsells only” in the Related Product element on the Product Detail page. Which should theoretically work, but I wondered if there were a more automated method that wouldn’t require me to set it up manually each time?