Comment by bix6

I am not an expert in these systems but it seems some have tremendous ability to link disparate data. At the simplest they have things like device IDs and emails from logged in users that make it easy; many users don’t or can’t opt out of the baseline tracking. If you do well now you’re special so they have to use other fingerprinting techniques. You can try and obfuscate which might change your ad package but they still know everything about you.

I think your belief that they can only target while using the app is naive. They can sell the data to aggregators for more sophisticated use.