The Facebook iPhone app asks for permission to track the user in this early mock-up of the prompt made by Apple.

“It seems that in the United States, at least, app developers and advertisers who rely on targeted mobile advertising for revenue are seeing their worst fears realized: Analytics data published this week suggests that US users choose to opt out of tracking 96 percent of the time in the wake of iOS 14.5.”

Source : 96% of US users opt out of app tracking in iOS 14.5, analytics find | Ars Technica