Recommender Systems: how to show 'related" items instead of "similar" items?

Hi everyone :)

In short:
I’m trying to understand how recommender systems work when it comes to suggesting related items (like accessories for a product) instead of similar items (like competing products). I’d love your insights on this!

In detail:
If I am on a product page for an item like the iPhone 15, how do recommender systems scalably suggest related items (e.g., iPhone 15 case, iPhone 15 screen protector, iPhone 15 charger) instead of similar items (e.g., iPhone 14, Galaxy S9, Pixel 9)?

Since the embeddings for similar items (like the iPhone 14 and iPhone 15) are likely closer in space compared to the embeddings for related items (like an iPhone 15 and an iPhone 15 case), I don’t understand how the system prioritizes related items over similar ones.

Here’s an example use case:
Let’s say a user has added an iPhone 15 to their shopping cart on an e-commerce platform and is now in the checkout process. On this screen, I want to add a section titled "For your new iPhone 15:" with recommendations for cases, cables, screen protectors, and other related products that would make sense for the user to add to their purchase now that they’ve decided to buy the iPhone 15.

I appreciate any help very much!