For open source messengers, you can check whether they actually encrypt your messages and whether the server has access to your encryption keys but what about WhatsApp? Since it’s not open source, you can’t be sure that the encryption keys aren’t sent to the server, right? Has there been a case where a government was able to access WhatsApp chats without reading them from the phone itself?
I think that photo goes against the claim that WhatsApp can decrypt or otherwise easily get access to message content
Also was that before the full encryption of the backups? Someone else posted a study about their backup encryption where they concluded that it at least seemed secure (with the caveat of it being a proprietary app).