I mean you are pressing a button to send them to the AI. It's like clowning on how Signal messages are supposed to be private and can't be read by anyone else, while you yourself are sending a screenshot of the conversation to others. Or inviting a journalist to your secret group chat...

The dubious part is the claim of privacy in Meta's AI.

So I think, but I'm not sure, this is for group chats. Group chats are only encrypted to/from the server because the server broadcasts the message to each recipient. As the messages are unencrypted on the server, they can feed them to LLMs.

This is different to Signal. On Signal it's your phone encrypting each copy of the message before sending to each recipient individually.