Have you been to an airport yet since it became mandatory? They actually have signs around stating it. I had similar thoughts as the GP about that.

It is called "TSA ConfirmID". https://www.tsa.gov/tsaconfirm-id

"If you are unable to provide the required acceptable ID, such as a passport or REAL ID, you can pay a $45 fee to use TSA ConfirmID. TSA will then attempt to verify your identity so you can go through security; however, there is no guarantee TSA can do so."

From https://thepointsguy.com/news/tsa-security-with-confirmid/ :

"TSA agents pull you aside for secondary screenings and to verify your identity. ... After looking me up in his system, [the supervisor] asked me a series of questions only I could answer (previous addresses and that sort of thing)."