The "e" in e2e encryption is a computing device, not the device's user's brain.

Right. So I send a push notification with the "silent" flag and encrypted content; the app receives it, decrypts the text, and displays the notification locally. Google/Apple has only ciphertext in their FBI/CIA/NSA-accessible databases.

I'm confused. You mean the iOS system notification would display the decrypted message in plaintext? Or do you mean the iOS system notification would display the encrypted message (i.e. it would be unreadable)?

The app decrypts the message and displays it via the system notification.

So in that case, the system has access to the plaintext, therefore the Alphabet boys have access to it as well. Unless, of course, you believe Apple isn't cooperating with them.

Am I missing something here? Maybe I'm missing a subtle detail.

A system like the one in "my phone's operating system". Do you assume that "Alphabet boys" have access to all parts of all Android file systems of all the phones ever produced?