[massel]

I expect that Signal encrypts the notification data prior to sending it to Apple, then decrypts it on-device using a Notification Service Extension – this is a common pattern to avoid trusting Apple with any sensitive data.

That would mean Apple stored the cleartext on-device after decryption.

[eggnet]

Signal doesn’t provide anything in the message other than… “there are pending messages.” Signal wakes up, fetches them, then generates notifications on the phone itself.