Earlier quoted context omitted.
What the difference between Meta's tracking pixel and Apple's IDFA?
From the top hit for IDFA (the wikipedia article): > Starting in iOS 14.5, iPadOS 14.5, and tvOS 14.5, users are prompted to decide whether to opt-in or out of IDFA sharing before apps can query it. This choice can be altered in Settings.[2][3] In May, 2021, Verizon-owned advertisement analytics company Flurry Analytics reported that 96% of US users opted out of IDFA sharing.[4]
And since you brought out the opt-out option, one can also block Facebook's trackers through uBlock and/or DNS filters.
The defaults are what matters. From the same Wikipedia article,
> Users can opt-out of IDFA via the "Limit Ad Tracking" (LAT) setting (and an estimated 20% do).
80% users never change the defaults.