The product recommendation section can be added on the product template. If you open the product page template you will see it added by default.
Simply click on the 'section' to open the settings.
On the right sidebar, the following settings will show:
Maximum products to show:
How many products do you want to show as recommended.products. The product recommendations will be loaded in by the Shopify Search & Discovery app.
Products per row:
How many products do you want to show in the row? When there are more products then the amount set on the row, the section will turn into a products slider.
Set the heading size for this section to be left or center.
Add the background to this section and adjust it according to your need.
Set the heading text for your recommend products section.
Heading font and size:
Select the font families and size for your heading.
Enable this option to have different styling for your heading.
The text section has the same customization settings like the heading once.
On mobile you can make this section as an accordion and adjust the background added to this section.
Bottom spacing desktop/mobile:
Set the spacing on the bottom for desktop and mobile.
That way you will get the amount of whitespace below the element you want. The default for desktop is 50px and the default for mobile is 0px.