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?
The better question is, do you trust meta at all? I'm sure they have a way to read everyone's chats and would gladly hand over yours to the government if they want it.