The list of E2E above is quite transparent. The notion of building a special version of the OS to target an individual is just not how the infrastructure works, and totally goes against the entire spirit of privacy that pervades everything you do internally.
Sorry to be blunt (and I am a big fan of Apple's pro-privacy shift of late) but nobody outside Apple can know that with any certainty.
Even the 2016 blackhat talk on youtube, which describes an elaborate signing mechanism for updates, doesn't preclude shipping targeted OS updates to individual users. Maybe I missed something though, and in that case I'd appreciate you pointing it out.
I can tell you that most people inside of Apple would be shocked if such a thing occurred. I doubt the code pathway / infrastructure even exists to do such a thing. There’s always the possibility of strange things happening that only the right 1-2 people know about.... although it’s probably have to be many more given the number of changes that would be needed to be made to propagate a special one off code signed OS OTA. That would likely have a whistleblower somewhere.
The reality is it’s way easier to just exploit a weakness that you can text someone [1].
But if you’re dressed in tin foil hat to toe, then there’s nothing that I can say to convince you. At that point I’d suggest not using any computing technology that you don’t personally build yourself and watch 24/7.
