Is it no longer allowed to open the windows with a ventilation system?

What does your wall structure look like?

Theoretically, modern silicone resin plasters and facade paints are supposed to be somewhat breathable, but this will not be sufficient to prevent mold 100%.

in modernen Häusern nur noch feststehende Fenster und Terrassentüren

This is also a big step forward in terms of burglary protection. You just must not forget to steal an emergency hammer from the city bus on occasion and then hang it in your own house on planned escape routes.

Theoretically, modern silicone resin plasters and facade paints should be a bit breathable, but that will not be enough to prevent mold 100%.

Marketing talk from the manufacturers. It doesn't help because there is a wall in between. No matter how breathable it is.

Theoretically, modern silicone resin plasters and facade paints are supposed to be somewhat breathable, but that will not be enough for 100% mold prevention.

...plaster and ... paint -- that says it all (ONLY plaster and paint are mentioned). Even today/again, one can build in a very modern way mostly with natural materials like straw and clay -- then you get "breathable" walls and a very healthy climate. But I think Heidi1965 does not intend that and it leads far off topic here