Currently, there’s no built-in method or API endpoint that allows you to list items that lack recommendations.
As a workaround, you could use the /recommendations endpoint and iterate through your catalog’s objectIDs, querying the relevant Recommend model (ie. related-products or bought-together).
If the API returns an empty hits array, that means the item currently has no generated recommendations.
Our full documentation for getting started with our API Clients can be found here.