I'm annoyed that this article doesn't explain at all 1) how governments are actually using push notifications to spy, 2) what apps they're using, and 3) how users can protect themselves.
The government is spying on me and you're not going to tell me how they're actually doing it? Not helpful.
Even that won't protect you. They still have analytics on billions of websites since they offer a robust free analytics interface for small webmasters, and have a paid tier for enterprise level websites. They still track everything that goes through Gmail and Gmail is used by billions of people. Your emails are still being read by Google every time you email someone who uses Gmail. Even if you refused to email a Gmail user, many small businesses use Gmail without you even knowing, passing their custom domain name through the gmail servers. Your web activity is still being tracked by Google every time you visit a website or use an app with Google analytics on it. Not personally using Google products, or not having a Google account does nothing to protect you from their tracking.
Edit: that's without even mentioning their Android OS.