Can you retrieve deleted messages?

IF you have not turned on iCloud Messages (Settings > your name > iCloud > Messages) and IF the messages are in your latest backup you can restore your iPhone and retrieve them. You will lose anything added since the date/time of that backup.

Restore your iPhone, iPad, or iPod touch from a backup - Apple Support

How do I retrieve deleted messages on my iPad and iPhone from iCloud? I do not have a computer. What data will be lost, if any? i.e. Calendar, notes etc.

I have not deleted messages on Messenger but I can’t see them anymore. The only ones gone are between a friend and myself. If she deleted them are they also gone for me? There’s valuable information I can’t retrieve