Thanks for the feedback.
Actually I have no use case for a specific app.
Instead, I'm interested in whether there is more specific information about who the "partners" named in the May 2019 iOS Security Guide are. The section "Safari Suggestions, Siri Suggestions in Search, Lookup, #images, News app, and News widget in non-News countries" says that in some cases queries are forwarded to qualified partners.
Therefore I am looking for whitepapers or something similar. Many thanks for any help!