With Search & Discovery, you can display pre-specified recommended products (related products) on the product detail page, but if they are placed at the bottom of the page, they may be overlooked. Therefore, by displaying these products in the pop-up notification after adding to cart, they will be more likely to catch the customer's eye, and you can expect to maximize upselling opportunities.
Example of setting to display recommended products in the cart popup notification when adding a product to the cart when using the theme "Dawn/Rise"

[Setup Method 1] Add "Accessories" to each product using Search & Discovery

[Setting Method 2 (for the Rise/Dawn theme)] Theme Settings: Set the cart type to "Pop-up notification" and add the "Accessories" block to the product information section of the product template.

[Setup Method 3 (for Rise/Dawn Themes)] Add a customized Liquid block to the product information section of the product template and insert the code.

