Thanks to the EU’s regulation that is forcing Meta’s hand to interoperable with third-party messaging apps, this security guarantee now means absolutely nothing.
End-to-end encryption is meaningless when one end is compromised. Either because a user has been maliciously duped into downloading a compromised third-party app that Meta now must interoperate with. Or due to government pressure on a third-party app that doesn’t have Meta’s legal resources to fight government coercion and overreach - ad hoc Chat Control.
Interesting because this is one of the arguments I’ve put forward against third-party App stores and people who claim (incorrectly, BTW) if you never download anything and stick to The App Store you’ll be safe.
You’re not safe if the other person’s device/Apps are compromised.