Similar product

Name: Similar product
Namespace and key: custom.similar_products
Content type: List - Product

In product setting:

Result:

Choosing the metafield (version 1.3.0)

The Shop similar product section reads this content through its Similar products metafield setting. The default key is custom.similar_products.

Keep the default key above and it works with no extra setup.
Or rename it: create the metafield under your own namespace.key (for example, your brand name), then set Similar products metafield to match.
Reuse on one page: create one metafield per copy (for example custom.similar_products and custom.similar_products_2) and point each Similar products metafield at its own key to show different content.

See How to setup Metafield in version 1.3.0? for details.