Privacy effects of disabling notifications through Android settings Assumption
My question assumes the following situation, that is what I could understand about Google's push notifications system. If I misunderstood anything, please correct me here.
When a web service wants to send a notification to a user who installed its app (client), it sends the notification content to Google's push notification server. The server then contacts the user's device instructing it to show the notification.
This system prevents user's device from continously checking for notification, that would cause battery drainage and other annoying side-effects. However, some privacy concerned people point out that it allows Google to access all the notification contents, including for example private messages.
Question
If I have an app (client) that manages* notifications on my device for a web service and doesn't have an option to disable them, the only way I can prevent them to be shown is through Android settings.
To my understanding, if I do so the web service (that doesn't know my Android settings) will still send notification contents to Google's server, thus allowing Google to know notification content, but the server won't send it to my device. So, disabling notifications through Android settings wouldn't have any effect on privacy. Is that right?
*I use the word &quot;manage&quot; because usually the notifications are shown if and only if the app is installed and it often has settings for them (sound selection, vibrate and so on); however, I don't know how much notifications depend on the app and how much on the system. Anyway, it looks to me that it is not very important for the question (but I might be wrong of course).
Push messages - what do they contain
What data each app receives via Firebase push notifications can be very different.
Some apps receive the complete message content as Firebase push notification to the user's app. In such a case Google can of course see the complete message.
Apps that handle privacy related content should use push notifications not as data transmission system. Instead they use push notifications just as notification for the app that new data is available on their own WhatsApp/Signal/... server.
Therefore for messenger apps I would expect that the push notifications may just contain e.g. a number the app processes and then knows that new data is available on the server.
Disabling notifications for an app
Regarding the question what happens if you disable notifications of an app in settings this also depends on the app:
The app itself can check if you have enabled/disabled a certain push channel. Therefore it is possible for an app to disable the notifications on server side so that no push messages are sent at all if you have disabled notifications for that app.
However a lazy app developer may not implement such a check. In such a case I would assume that all notifications are sent as before but just ignored by your device.