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?
EU usually frowns upon that though. Sure, the fines are so small that it’s negligible for Meta, but there should be some fines. But all I find via quick googling are this year’s sanctions over personal data processing in Facebook/Instagram/WhatsApp. The nature of these data is not clear though.
I am not trying to say that WhatsApp is safe to use, mind you. I am pretty sure they will hand over all the info along with encryption keys at first government’s request (or any other highest bidder for that matter), but that’s only my perception of them as a company, with no hard proof at hand.
The EU has been trying to outlaw encryption for most of this year.
"The EU" isn't one singular person or party or state or whatever. There are some people who are trying to outlaw it but that doesn't mean that they're the majority or that it's even legal to do.