If you aren't using Apple's App Tracking Transparency, read this immediately

One somewhat under-appreciated setting on the iPhone and the iPad is the ability to enable or disable app tracking. As part of Apple's App Tracking Transparency initiative, which it introduced in 2021's iOS 14.5, iPadOS 14.5, and tvOS 14.5, users are able to dive into settings and permit or deny third-party apps from tracking activity from across apps and websites.

Source : https://www.pocket-lint.com/how-to-control-apple-app-tracking-transparency/