Our recommendation engine includes by default any product available in the feed.
Integration modules or your custom product feed differentiate main products to those that are simple variations. If you only want to display main products you can do it for each recommendation block separately or you can do it at account level.
Always check the data type available in your catalogue! Providing wrong values here will be either ignored or not show any products. Go to Setup -> Product Feed, check a product and look if it has “main” attribute and what is the data type.
“Main” is a product attribute that has only 2 values: 0 or 1. In order to display only those with main 1, you just enter a valid JSON object, as below. Add this in the include section of Products&Categories