Without evidence of this “special arrangement” I don’t see why anyone should believe you. You made a claim that is directly contrary to WhatsApp’s published materials and they have a lot to lose if you are correct. On the other hand, if your accusation is false, it’s tantamount to libel.
How's this? Not sure if it's the same issue but it's much more damning than the one I knew about. https://www.techspot.com/news/112232-federal-agent-whatsapp-...
You know how I found this link? Googling WhatsApp encryption backdoor. You could have too.