Telling a German to open windows is like telling a bird how to fly. Stoßlüften is down to a precise science here.
But it doesn’t matter with the temperatures and building construction style. They retain heat like crazy. It’s not getting cold enough at night for the buildings to lose all their thermal energy, even creating air flow through the building with a fan. Source: me with all my windows open in a 4th floor apartment with the inside temperature sitting at 28°C at near midnight.