That's DNA, not facial structure

IIRC there are an estimated roughly 1 Billion different allele combinations that deal with appearance so hypothetically you should have 6-8 doppelgängers somewhere in the world.

There’s no objective measure for quantifying similarity. We can measure relative similarity, though—but that scale will vary depending on what it’s relative to.

We could measure genetic similarity relative to a typical unrelated person, or relative to the nearest non-human animal, or relative to the most distantly-related living organism, or relative to random noise. (And you can do the same for facial similarity.)

Humans do have really low genetic diversity compared to most other organisms. Not as bad cheetahs though!