Generally, most devices don't encrypt/protect your data with that 6-digit PIN directly. They store the important secrets like device encryption keys in some kin

Generally, most devices don't encrypt/protect your data with that 6-digit PIN directly. They store the important secrets like device encryption keys in some kind of secure enclave/processor that does things like rate limit the PIN attempts to prevent brute-forcing. What the fingerprint or face scan is doing is just unlocking that secured data a different way.