Face ID data, including mathematical representations of your face, is encrypted and onlyApple also specifies that it has trained a neural network to “spot and resist spoofing” to defend against attempts to unlock the device with photos or masks.
available to the Secure Enclave. This data never leaves the device. It is not sent to Apple, nor is it included in device backups. Face images captured during normal unlock operations aren’t saved, but are instead immediately discarded once the mathematical representation is calculated for comparison to the enrolled Face ID data.
The company goes on to say that the chance of a random person being able to unlock your phone because their face fooled Face ID is approximately 1 in 1M.
What strikes me here is the Apple focus on a "random person," but what about a relative with similar facial features?