Three methods actually work, in this order: the Recently Deleted folder (past 30–40 days), reading an old computer backup (any age — without restoring it), and restoring an iCloud backup (last resort; it erases the phone). Everything else — "deep scan" apps, no-backup recovery tools — is marketing. iPhone storage is encrypted; deleted means deleted unless a copy exists somewhere.
Needs iOS 16+. Messages deleted more than ~40 days ago won't be here — keep reading.
If the iPhone was ever backed up to a Mac or PC before the messages were deleted, those messages are still inside that backup. You don't need to restore it — read it directly:
Settings → [your name] → iCloud → Manage Storage → Backups shows what exists and when. Applying one means erasing the iPhone and losing everything since that backup — photos, messages, all of it. If you must: restore onto an old spare iPhone instead, then back the spare up to a computer and read it with Method 2. Never sacrifice your live phone to check for old texts.
About "recover without backup" apps: the App Store and $60 desktop tools promising no-backup recovery all end up reading the same three sources above. iPhone storage encryption makes scanning deleted space impossible — that's a hardware-level fact, not a software gap.
Messages that survived one deletion scare deserve better odds. Export the conversations that matter to PDF (guide), and back up quarterly (how). If they're for a legal matter, use the court-ready format: printing texts for court.
On Android? Deleted-message recovery for Android.