Before iOS 16, you had to restore your iPhone from a backup to retrieve the message. Thankfully, this isn't the case anymore, and you can restore deleted messages right within the Messages app ...

Use iPhone's Notes app collaborative feature to send private messages that look like regular note-taking to anyone watching your screen.

Though you can lock and hide apps on iOS 18, which includes the Notes app, you might want to add more security to individual entries by locking notes.