By your terminology, all iOS devices are “compromised” by default from having non-e2ee iCloud Backup enabled by default.
Signal chats on iOS are stored in a storage class that cannot be backed up or exported from the device.
https://en.m.wikipedia.org/wiki/PRISM
From the front page of the Times today, they are renewing the law that says they have to do it without a warrant (FISA Section 702, aka PRISM).
https://www.nytimes.com/2024/04/12/us/politics/surveillance-...
You’ll note that this is regularly and frequently used by the FBI against domestic users (such as BLM protesters). Apple processes these FISA demands on over 70,000 user accounts every year, and the number is increasing. (That’s just the count for the warrantless FISA stuff - search warrants are a different (larger) figure.)
They also expanded it to allow them to search Apple’s data on people entering the US as visitors.
> The House also passed several other significant amendments. They included allowing the Section 702 program to be used to gather intelligence on foreign narcotics trafficking organizations and to vet potential foreign visitors to the United States; empowering certain congressional leaders to observe classified hearings before a court that oversees national-security surveillance; and expanding the types of companies with access to foreign communications that can be required to participate in the program.
iMessages are backed up in duplicate - once on the sender and once on the receiver. You can only control e2ee for half of it, so your conversations are still under surveillance unless everyone you message with has also turned on ADP.