NOTE: You can make the configuration of blog related product rules if you use Blog Plus or Blog Extra extension.

In order to set the related product rules, you have to choose a blog post you are interested in, go to its configurations in Magento 2 admin panel and find the Related Product Rules section. Here you can set the related rules based on product attributes like category, sku, price, etc. If some attribute is missing in the rules please check the article "How to add product attribute to rules conditions".

Magento 2 Blog Post Related Product Rules

Once you have finished don't forget to press the Save button.

After saving these products will be automatically added to the related products list and marked as Related by Rule.

Magento 2 Blog Post Related Products List

Besides, they will be frequently updated automatically by cron.

Here is an example of how related products to be displayed on the storefront.

Magento 2 Blog Post Related Products