This is about what dedicated murderous goverments can pull off using conventional means.
The death camps were a practical end result of how much manual labor was required to line thousands of people up and shoot them dead. That’s what they were doing in Poland, to such extremes that is was literally more efficient to build gas chambers.
https://en.wikipedia.org/wiki/Babi_Yar
The Nazis were still killing people in other places at the same time, so the deadliest day is probably much much higher.
The scale of the Holocaust is hard to imagine. Even just looking at very specific suranmes, there are 23,000 killed with the surname Rosenberg, 12,000 with the surname Adler...
https://collections.yadvashem.org/en/names/search-results-na...