I never bought into the German citizens claiming they “didn’t know” about the Holocaust. There was far too much infrastructure to keep it secret. Not only did the crematoria engineers and employees know, I believe the greatest source of common knowledge of the camps was from the railway workers. Every guy who ever made the “Auschwitz run” had to know what was going on. So all of the railway workers knew from what they heard. And since everything moved by rail, the number of people employed in the rail industry had to be quite large. Everyone had a family member or knew someone who worked for the Reichsbahn.
Yeah, they all knew. But it was too horrible to admit it to themselves.
I'd put it this way:
Some knew little or nothing.
Many more knew "something".
Very, very few knew everything.