The most famous forms of Holocaust denial and revisionism tend to focus on Jews, casting doubt, for example, on how many were exterminated in the camps. But denying the impact the Nazis had on the other groups they targeted, including queer and trans people, disabled people and Romani people, is still Holocaust denial. Maybe someone should tell J.K. Rowling.
Pro tip: used book sales do not generate royalties. I bought the full set of HP from a local used bookstore with no guilt.