How to bulk link between products?

In order to set similar and related products for a product in bulk, go to the list of products, then select the products for which you need to set Cross-sell.

In the menu that appears at the bottom of the screen, click on the "Cross-sell" button and select which type of Cross-sell you will add:

Add “Add related products”;
Add "Add similar Products".

In the window that appears, specify the products to be added to the selected section.

More information about adding products can be found at the link How to establish a link between products (this product buy with or similar product)