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 blog related product rules:

1. Choose a blog post you are interested in and go to its configurations in Magento 2 admin panel.

2. Find the Related Product Rules section.

3. 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

4. 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 are displayed on the storefront.

Magento 2 Blog Post Related Products