Unfortunately, in theory, _everything_: law enforcement stopped pushing for decryption because Apple became responsive to requests for icloud backups, which are _not_ encrypted, and no plans to. Word on the street is that was a negotiated understanding with gov't
In practice, Apple says they use the following data for targeting: search queries, news articles you've read, any content bought through their various store fronts, App Store searches, and app usage data and using it for targeting. Some of this is un-differentiable for privacy/needs to be stored server side, the Apple docs neither mention this distinction nor differential privacy at all, and there's no public indication any of this is covered by differential privacy
In practice, Apple says they use the following data for targeting: search queries, news articles you've read, any content bought through their various store fronts, App Store searches, and app usage data and using it for targeting. Some of this is un-differentiable for privacy/needs to be stored server side, the Apple docs neither mention this distinction nor differential privacy at all, and there's no public indication any of this is covered by differential privacy