It's important to remember, they aren't stopping them from doing the overly-intrusive cross-app tracking, they just make you actively consent to an app allowing that tracking.
Apple is doing the classic "we don't share with third parties, we just collect a shit ton of data from everywhere and then make people buy our data indirectly via our ad sale services" like google and facebook do today. So it's not shared with third parties, but because of their scale it might as well be in effect size .
It's called App Tracking Transparency and there is a scary prompt when Facebook/others do it. It's called Personalization and a friendly prompt when Apple does it.