I remember reading an article where the government and Google were able to read notifications and record them from every android device. I wonder if Graphene might have patched this problem, and if not, do they have any plans to do so?
I've never worked directly with FCM, but that's my understanding of the issue. I don't know about WhatsApp. But it may do the same thing as Signal where the notification is just a wake up call and then the app connects directly to the WhatsApp servers to get the actual message.