Comment by svpk

I think the confusion here is that Signal does in fact encrypt the notification in transit [1]. The FBI had access to the user's unlocked iPhone and went through the notification history on the device. The issue the user faced is that even though they deleted the signal app they were unaware that iOS (and Android by default) retain a database of past notifications even after they're dismissed from the notification pane.

[1] Well actually they just send a blank notification, the signal app then reaches out to the signal server for the actual encrypted message content when it receives the empty notification.