> Apple and Google have put themselves in the middle of most notifications, causing the contents to pass through their servers, which means that they are subject to all the standard warrantless wiretapping directly from governments, as well as third-party attacks on the infrastructure in place to support that monitoring.

>If you don't want end-to-end messages made available to others, set your notifications to only show that you have a message, not what it contains or who its from.

This incorrect on two counts:

1. As per what you wrote immediately before the quoted text, the issue was that the OS keeps track of notifications locally. Google/Apple's notification servers have nothing to do with this

2. It's entirely possible to still have end-to-end messaging even if you're forced to send notifications through Google/Apple's servers, by encrypting data in the notification, or not including message data at all. Indeed that's what signal does. Apple or Google's never sees your message in cleartext.

If Signal wants to show you a notification with message text, it needs to put it on the screen through an OS service. That service was storing the plaintext on the device.

You are correct, but you omitted one complication: Clients trust Google's and Apple's servers to faithfully exchange the participants' public keys.