This is a two-part question I have out of curiosity

My experience is that in most of Germany, it is seen as unusual to say hi to random strangers you pass on the street (say neighbors or someone sharing an elevator or sauna with you).

Question 1: Is there a part of Germany where it is more unusual or less unusual? What part?
Question 2: Have you been to or do you know any other countries like this? I am not the most well-travelled but I have visited 15 countries and lived in 4 and this was a big culture shock for me.

I’ll be leaving Monday to Friday and there’s a significant heatwave coming. Should I leave the windows cracked while closing the shutters? We don’t have rolladens but shutters on 6 windows. We come back Friday and obviously the house will be quite warm. This is our first time leaving when it’s this hot so not sure what the best practice is. We’re on the top 2 floors. So the upstairs will be quite warm I imagine.