So, if you want to have any sense of a service respecting you, it should be hosted on a server you can control?
No difference at all between the server of the world’s biggest advertiser and a server by a company that opens itself for audits and is in a country whole laws require no bullshit? Are you sure those two are the same? All or nothing?
You can’t encrypt anything without a key. This is the key. If it wasn’t in plaintext then it would be encrypted. Then you’d need a key for that. Where do you put it?
Phone OSs have mechanisms to solve this. Desktop ones do not.