Read the “Learn more…” link at:
Settings >> Privacy and Security >> Tracking
You can disallow apps to request to track, and in that case, they will be blocked from accessing the Advertising Identifier.
There is also this statement, but it’s unclear what data it applies to:
App developers are responsible for ensuring they comply with your
choices.
There are also statements about kinds of sharing that are not considered tracking.
There is a similar statement at:
https://support.apple.com/en-us/102420
If you choose Ask App Not to Track, the app developer can’t access the
system advertising identifier (IDFA), which is often used to track.
The app is also not permitted to track your activity using other
information that identifies you or your device, like your email
address.
Some Apple privacy protections are enforced in OS code, some are enforced at app review time. The nutrition label and the ask apps not to track control are the best overall resources for controlling access to the Advertising Identifier, but even though it is disallowed it is possible an app can use other means like device fingerprinting to track you. so the best solution is not to use apps you do not trust, or apps from a developer you do not trust. In all cases, minimize the amount of personal information you share with an app. And whenever possible, use a privacy-friendly web browser rather than an app for less leakage.
