Attic problem. High humidity - Controlled residential ventilation?

Could work, as long as it doesn't rain or snow in during wind or storm and the windows don't blow away during the storm.

Could work, if it doesn’t rain or snow in when it’s windy or stormy and if the windows don’t blow away during the storm.

I would then set the roller shutter to half so there is some protection on the weather side.
The temperature at the top would then naturally match the outside temperature. But since it was "insulated" from top to bottom, I shouldn’t get the cold from above either.
Could mold form on the windows due to constant tilt ventilation since air only comes in there? Or is better airflow ensured by cross-ventilation through the window directly on the opposite side?

I wouldn't expect any mold there.

The thing with the windows is now the temporary solution until we have enough money for a controlled residential ventilation system. Heating is out of the question because only underfloor heating would work up there, but as long as no one lives there or it is finished, it doesn't make sense. And putting a stove upstairs that only heats there, basically for nothing, is also stupid. So we will have to get a residential ventilation system after all.

The fundamental mistake is that it was done halfway. Either completely or not at all. Not at all means that it is a true cold floor without any insulation, as ours is. It is dry, airy, ice cold, at least for now. It constantly gets fresh air through the roof soffit gaps and through the tiles. In addition, it has a Velux with a ventilation setting. Completely would mean insulating and heating this room so that it could be lived in. Like other living spaces, it would need to be ventilated. Because modern houses are simply as airtight as plastic bags. That would also work. Halfway means what happened here. Insulated, wrapped up, sealed, but neither heated nor ventilated. So there will be cold air standing there and condensing on the panes, etc. The remedy is forced ventilation. So, trickle vents in the windows, plus mounting a Helios exhaust fan that extracts air up there, which is sucked in through the trickle vents. And depending on the weather, there will also be a draft. Karsten

Exactly for this reason, we heated the DG (radiators instead of underfloor heating) and included it in the controlled residential ventilation. The heating is set to 16 degrees... so not much heating is needed. Humidity at about 40%.

Our architect had pointed out this exact issue to us beforehand.