Restore text messages
Why aren’t text messages backed up, especially when they randomly disappear. It appears this is not a backup feature.
I’ve tried turning messages off then turning my phone back on but the messages are still gone.
iPhone XR
IF by turning message on you mean by this Keep all your messages in iCloud - Apple Support it is not part of the backup.
all message is part of the icloud or itunes backup What does iCloud back up? - Apple Support