Draft at the corners of the windows?

Sorry I might not always have the terminology quite right, maybe the word Bauträger was wrong. The house comes from a well-known prefabricated house manufacturer Massa Haus, whose services also included installing the windows (as I understand, still in the factory during the production of the house walls).

Massa Haus is a house manufacturer specialized in shell construction houses but manufactures in Europe. I cannot explain the condition in the pictures. It does not look like new (i.e., built in 2023), as hardly the second set of windows would be installed by now.

According to which standard was the house built? I think I read somewhere about 2 years. We had our expert here again last week. He conducted an individual leak measurement with an anemometer while 50 Pascal underpressure was generated in the house. I learned that anything above 0.5 m/sec is already considered too much. And with us, you can sometimes only see a slightly too short plaster strip on the window. I would complain about that if I were you, that should not be the case. Do you have electric roller shutters/blinds? Then check if they are connected to a socket and also poorly sealed.