Mold on uninsulated flat roof equipment room

I have exactly the same setup and the same problem, but I am now in the first year. I have also installed a bathroom fan that monitors the dew point for about a month now; it only ventilates when the absolute humidity in the room is below the humidity of the surroundings. This means the fan currently runs about 40-50% of the time, especially during the day. I am curious how this will behave in winter. However, the ventilation does not seem like a good solution to me at the moment. I would also prefer a permanent solution through insulation or similar.

I have decided for myself to take the official route through the construction company and file a defect report. What do I have to lose? So far, I have shown goodwill and tried to handle the problem myself, but without success. Let's see what happens. The main thing is that the report is submitted within the five years.
At another point, the construction company had already repaired free of charge, but that defect was undisputed (Rollladenmotor hat wegen fehlerhaftem Einbau sein eigenes Kabel aufgewickelt und zerrissen).

We had sent a notice of defects to the construction company in this matter. Of course, the issue is not being addressed. It is still being claimed that we must ensure, through heating and ventilation, that the humidity does not rise above 60%. I believe such statements are actually acceptable for living spaces, but for unheated equipment rooms??? I am seriously considering involving an expert. However, if that does not work either, I will be stuck with costs that may be higher than a new roof. What would you do?

Hmm, the question is to what extent one might already get some information for little money from the Bauherrenbund or similar. I would also find it difficult right now to assess whether this type of construction is not actually state of the art, even if it is a really poor state.