So your partner only needs to have had 1 single app from the list that sells user data to a data aggregator for this to work. They do not need to have installed some special app.
Here's a random Slate article about apps getting your data and selling it to aggregators/brokers, who sell it to third-parties (you, or I, could be one of those third parties).
> How Shady Companies Guess Your Religion, Sexual Orientation, and Mental Health And sell that data to the highest bidder.
https://slate.com/technology/2023/04/data-broker-inference-p...