@Gorby,
That's not how any of that works.
If (a) government(s) want to identify JW in their population by that method, they need either
- Access to the user data for all phone accounts from Google and Apple, or
- Hack into the phones of every citizen to see who has JW app installed.
The latter is ridiculously time consuming and expensive, the former might be remotely possible for the USA but hardly for anyone else.
Of course, if a government were to confiscate an individual's phone and find the JW app, that's a different story. But that's hardly a scalable method of mass identification of JW.
Interestingly though, Watchtower might be able to track users who have installed the app if they would build that possibility into their app. Right now the app doesn't seem to be able to send some data back to Watchtower; the app doesn't have any permissions from the phone's operating system...