Proper ventilation behavior without controlled residential ventilation

yes, rather the usual case when you don't have controlled ventilation... most people don't ventilate properly and regularly. Often there are still things on the windowsills, so you might tilt the window briefly, but not for too long, because there is a draft.

Humidity is just one thing, the other is CO2 and the quality of the breathing air. I used to have headaches very often in the house, with [Lüftungsanlage] almost never. The PPM value is always around 500 - 700 in our place.