Since 1997 we have a proper warm roof (18cm insulation between rafters; vapor barrier on the room side and covered with plasterboard) and the intermediate ceiling is also insulated (vapor barrier towards the living spaces). On the beams there is tongue and groove boarding.
In the gable we have a round window (which is rarely open) and a completely normal hatch with a pull-out ladder (so no thermos or anything like that).
The whole thing was planned by the architect and carried out by the builder.
No moisture problems or mold or anything else could be detected yet
(It should be mentioned that the plasterboard has a moisture-regulating effect)
From my point of view, this is not a proper execution. Your attic is not heated, if I read that correctly, so you also do not have a warm roof in the proper sense. With the insulation of the top floor ceiling you have a significant temperature difference between the upper floor and the attic, and thus also a higher vapor pressure difference, meaning moisture transport.