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?
People got arrested for WhatsApp messages in my country so there is a backdoor built in no question
That's mostly group chats and someone from the group showed the comments to the police.
Dunno