I've had basically the same conversation with my sister who lives in Albania. I just want to use something encrypted like signal but she just refuses and says it's either WhatsApp or Facebook messenger. Cause of that I barely talk to her.
Btw it wouldn't even matter, since the encryption happens in the client app. The server basically just passes around encrypted pieces of data between devices.
Here's the trick (maybe):
"Don't you know that WhatsApp is owned by Meta and collecting information on your chat metadata (who you chat to, when, your contacts, their contacts)."
Tell them to get Signal. If there's any country on this planet where convincing people to use Signal is easier, it must be Germany. GMaps streetview was banned there until recently, everyone uses fake names on Facebook, if they even made one in the first place.
They would say that at this stage. They are still working on getting the law overturned by courts and threat of shutdown mobilizes people against the law in a way that selling it wouldn't.
When the time comes to shut down they will probably do some paper work fuckery that technically makes it an Irish company but doesn't change the people in the company.