The claims 'there were literal nazi flags' (see https://cdn.vox-cdn.com/thumbor/8a1wytwIU2Ic52sok2ly14RUQNM=...) seem to based on the very broad assumption that Confederate, Kekistan, upside down US flags, 'release the kraken' etc flags are Nazis.
See https://qz.com/1953366/decoding-the-pro-trump-insurrectionis... for an example.
Update: this comment has been been flagged, but let me point out:
1. The comment was 'there were literal nazi flags'. We are still at 0 nazi flags.
2. The 'six million' shirt pointed out by Griffinsauce below wasn't from the Capitol: https://forward.com/fast-forward/461761/fact-check-the-6-mil...
The guy in the Auschwitz hoodie is a nazi and obviously an even bigger moron than the other rioters but maybe we'd be able to find out more about actual extremists if we didn't label everything we don't like as extremist?