As far as I know, there is no neo-Nazi song that is illegal in the US. I can buy Mein Kampf, I can sing whatever I want.
Back when Substack wasn't banning Nazis, more than one person told me that that was definitely the right way to do it, and pointed to laws in countries like Germany that prohibited Nazi content as an example of a good approach (sometimes, for some reason, claiming incorrectly that the US had the same laws).
When I said that those laws would invariably classify speech that the ruling party didn't like as "hate speech," they told me I was talking pure nonsense and that they were only classifying actual hate speech, so there was no problem.
Guess which country in the Schengen Area has classified speech against Israel as "hate speech" and prevented a doctor from coming to a university and giving a speech on what he witnessed in Gaza.
The point is not that Nazi songs are okay. The point is that people are going to sing what they want to sing, whether their songs are good things or bad, and that laws telling them they can't is (a) a big waste of time in the big picture (b) a lot more likely to be used against songs that are on the right side of history than the wrong side.