Text messages
Is there a way to restore a deleted text message thread without restoring your phone to factory settings
iPhone 11
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Restoring your device to factory settings would leave you with a phone that had on it exactly what it had when you first took it out of the box. It would not have your texts on it.
If you're using iCloud syncing for Messages, once you delete a message, it's gone. If you're not using iCloud Syncing and you have a backup that contains your messages, you can try restoring the phone to that backup.
Restore your iPhone, iPad, or iPod touch from a backup - Apple Support
But really, the likelihood is that once you delete messages, they're probably unretriveable.