This is correct. Message content is encrypted, and only readable from either an unencrypted backup on iCloud or if one of the message recipients reports your me

This is correct. Message content is encrypted, and only readable from either an unencrypted backup on iCloud or if one of the message recipients reports your message (their client then sends the message to Meta unencrypted). Message metadata is available to Meta. All I can say is.. if your threat model has to account for metadata like this than you have a whole lot more to account for than just WhatsApp or Signal.