I asked this of myself. With iOS 16 I see you can now retrieve deleted messages from the app but they will be gone permanently after 40 days.
I wanted messages a year old and I understand even with regular back ups, they’re gone forever. I got that info via Google searches iPhone messages specifically.
I looked into these lost data retrieval software specialists but I couldn’t find one capable although I did retrieve some very old email addresses, photos, music, word and excel documents which I thought I’d lost preTimeMachine.