I have a passport and it was one of the IDs I took with me. They did not accept it because the name did not match my DL.
I have never taken my passport for travel in the US because I don't need it. I have never had an issue with using my DL as ID for security at the airport, so I didn't take my passport for this trip. I have flown multiple times since Real ID was required with this license and no issues.
ETA - I find it absurd that my DL with a name that does not match my birth certificate or marriage license could be used to get my passport, but my passport could not be used to get my Real ID license because it did not match the name on my birth certificate or DL.