I don't want to debate the Holocaust. But Hibiki lists the sources for the population estimates, your source does not disclose the origin of their figures. More from your source:

The Holocaust is the best documented case of genocide. Despite this, calculating the exact numbers of individuals who were killed as the result of Nazi policies is an impossible task. There is no single wartime document that spells out how many people were killed.

The evidence is lacking and yet

Holocaust denial is any attempt to negate the established facts of the Nazi genocide of European Jews. Holocaust denial and distortion are forms of antisemitism, prejudice against or hatred of Jews. Holocaust denial and distortion generally claim that the Holocaust was invented or exaggerated by Jews as part of a plot to advance Jewish interests

Don't dare question it or you're transphobic anti-Semitic.