House purchase - Fogging, mold? Or what is that?

Hello,
We intend to buy a house. Built in 1998, solid construction.
During the viewing, we noticed dark discolorations above the windows in the dining room/kitchen. Attached is a photo of it. To make it easier to see, I increased the contrast and structure. In reality, the wallpaper is white and the spots are not immediately noticeable.
Maybe someone can help me figure out what this might be? What stands out is that apparently the roller shutter box is not affected, but it is exactly around it. Thermal bridge?
Thanks in advance.
(For safety, we are also looking into an IHK expert, but they probably won’t be available at short notice...)
Best regards
Mika

Depending on the type of construction, the area of discoloration will most likely be the uninsulated joint between the roller shutter box and the masonry. In addition, unplanned convection is to be expected here. Cold outside air penetrates almost to the inside of the outer wall and causes significant cooling of the wall surface. Condensation from warm, humid indoor air is to be expected, as well as dirt deposits. Where is the object located? I provide property purchase consulting nationwide, preferably so far in NRW/RLP/Hessen. I would be happy to send you more information by email.

Thank you for the quick response. The house is located right at the North Sea, on the border with the Netherlands. So presumably no insulation (or only poor insulation) is installed in the roller shutter box? Could that be mold? Best regards Mika