I'm not trying to be snarky, but I don't know how you could miss the backup feature[1] of iTunes (now built into Finder on Mac), given it's been a feature of the iPhone ecosystem well before iCloud was even a thing.
You are right that data in the Secure Enclave (e.g. TouchID / FaceID) is not backed up. Developers also have the ability since iOS 5 to mark certain data to be excluded from backup. But other than this the local backup is a complete dump of the device.