And once they get sufficiently interested, they can crack pretty much anything the market can come up with.
So if you're trying to hide stuff - old school is probably best, innocuous code-word language stuff, keep communication to a minimum, leave phone at home, etc, etc.
That's why I use Signal to chat with my wife and parents, and pretty much no one else. Secure apps need to become mundane so they don't draw attention, so I prioritize using them for mundane things.