Also, this app uses photos from a combination of government databases, but there are millions of citizens without photo ID who won't show up in any of them.

Social media datasets are likely in use.

https://en.wikipedia.org/wiki/Clearview_AI

My friend (who has an identical twin) was joking about scanning himself into Cameo mode on Sora and making some goofy videos and saying they were his brother.

There is no scientific proof that fingerprints are unique, either. Like a lot of forensic science, it's just accepted wisdom.

I think the scientific consensus is that they are NOT unique. I seem to recall there’s something like a one in five million chance of collision. (Recalling from memory so please verify, I recall thinking that in a large city there’s likely to be another person who’s fingerprints could be mistaken for yours)

IIRC, someone was accused and arrested for murder who lived across the country and couldn't have possibly committed the crime based on fingerprint match.

A book to read on the history of surveillance technology, starting with "pass papers" for slaves to finger prints:

The Soft Cage - Surveillance in America: From Slavery to the War on Terror, Christian Parenti, 2003

https://archive.org/details/softcagesurveill0000pare