As someone of German ancestry, I can attest that this type of slovenliness is not a typical trait of Germans, then or now. Germans tend to pride themselves on their cleanliness.
Timekeeping and hygiene are not fucking ontological traits you fascist fucking freak
Fun fact: The Nazi propaganda film The Eternal Jew used unflattering footage of impoverished Jews living in Polish slums to make the claim that Jews enjoy living in filth, unlike the clean and tidy Aryan master race.
It wasn't really nazis being bad at science, it was purposeful. Nazis did know that people who get lice and typhus epidemic wouldn't have those if they weren't living in absolute poverty. They even did same later in war when they make things even worse by locking Jews in ghettos without food and water and on 10% of needed living space, then they published posters in Polish to incite Poles agains Jews (also note the person who made that poster was definitively native Polish speaker)
I am a German today, my ancestry is nothing but Germans for at least 4 generations and my flat is a bit of a mess. I need to vacuum and dust and put things away. But I won't, no for a while longer at least. I washed my dirty dishes today and empties my overfull trash bin. That's gotta be enough.
Not that it matters at all, these genetic arguments are stupid and normalize thinking about everything in terms of race.
Germans also used to literally pick through their own feces as a matter of health. It's not that they are clean, it's that there is a certain class-based anal-retentive expectation. I've never met people more consistently sloppily hammered during the day than Germans (outside of maybe Wisconsin).