Installing NetGuard was revelation regarding the amount of tracking in most Android apps.

You can configure it to block access by default and notify you every time an app attempts a new connection. And it rings all the time.

Some software call home at 4am every day, other every hour, some send data to a dozen "analytics" services - services that I never opted-in for, which shows how few apps respect the RGPD.

At least most apps still work when those are blocked, and NetGuard allows you to block connections to Google servers except for Google Apps, which network firewalls and DNS solutions can't.