Face Unlock is pretty much easy to use and fairly secure. The face locking system work through a piece of software that can match a human face in a digital image to a database image. Learn from here whether Mi A2 contains this feature or not.
Xiaomi Mi A2 Face Recognition
No, Mi A2 doesn’t have a Face Unlock of its own. Previously this feature worked on Mi A2 through the google smart lock, but in April 2020’s update, Google removed the face unlock feature from the smart lock. So now, there is no in-built way for face unlocks in Xiaomi Mi A2.