Hi @benknaani,
I have read several posts on the subject about this matter and you always referred to the WooCommerce page but there is no real solution there. Related products do not show correctly on the product page.
Related Products is a section on some templates that pulls products from your store that share the same tags or categories as the current product.
These products cannot be specified in the admin, but can be influenced by grouping similar products in the same category or by using the same tags.
Cross-sells are products that you promote in the cart, based on the current product.
Up-sells are products that you recommend instead of the currently viewed product.
I’d say the closest thing you can use here is the Up-sells.
You can learn more about it here:?https://woocommerce.com/document/related-products-up-sells-and-cross-sells/.
My expectation in the parent category is to show products related to each other and it always shows related products from the main category. What can be done?
I’d also like to dig deeper on this part. Can you share more details, please? For instance, I’m looking at the product you linked, these are the related products I see for it: https://prnt.sc/pefAnAD6iedz. I see they’re mostly from the category “Top / Base” (the parent category) is this what you mean?
If this is the case, please remember the related products can be influenced to some extend, but cannot be manually set. You’d be better suited using the up-sells option, or a third party plugin to handle the related products better to your liking! A quick Google Search will lead you in the right direction!
Cheers!
-OP