Sure. But if one country (or one group of countries) legally requires Apple to do this worldwide and another country (or group of countries) legally forbids App

Sure. But if one country (or one group of countries) legally requires Apple to do this worldwide and another country (or group of countries) legally forbids Apple to do this even within their own national borders, then Apple has to decide which country (or group of countries) it cares more about. It's not obvious to me how that would shake out, but the UK certainly can't assume it would like Apple's decision there, especially since seeming to care about privacy is an important part of Apple's marketing brand.