Moisture in the attic. Heat comes from the interior wall.

A warm spot in the cold roof is not a problem but a cold spot in the warm area.
In other words, condensation / mold can occur at the top of the wall inside the room.
Why something is damp there has other causes: hole in the vapor barrier or not properly connected or completely forgotten, or hole in the roof or or or..

Condensation forms in the gap between the brick and wood. Heat and the cold surface of the wood are responsible for this. When the brick is covered with boards (loose), the entire insulation around and over the brick becomes wet, mold is unfortunately inevitable here.

Is that even proper for a cold roof? Since the floor represents the thermal envelope here, there should not be such a thermal bridge according to my understanding

I don't think it should be like that, of course, but I can't say exactly what was done wrong.

Do I understand correctly that the interior wall (brick) extends into the cold roof? Are the interior walls not normally below the vapor barrier (foil)? With us, the walls extend up to just below the vapor barrier foil / roof beams.

Yes, that's how it is. The brick serves as a support for the purlin and is unfortunately not insulated. That can't be right, can it?

yes, that's how it is. The brick serves as a support for the purlin and is unfortunately not insulated.
That can't be right, can it?

I am a layman but I know a little about it. We also have a cold roof. The roof (rafters) rests on the purlins. These, in turn, rest on the exterior walls. These walls are made of bricks, but due to the loads, at all four corners of the house there are so-called ring beams made of reinforced concrete, somewhat encircling, inserted below the purlins. As far as I understand, the roof therefore does not rest on the interior walls but on these ring beams. Our roof beams are then basically the ceiling of the upper floor. Below the beams, a foil is stretched (vapor barrier). This is partially penetrated by empty conduits or ventilation pipes, chimney, etc. Then sealed with flexible tape.
Between the individual roof beams, the insulation (mineral wool) is stuffed. The roof is then clad from below with drywall.

But while writing, I vaguely remember that we have an interior wall in the bathroom that is structurally relevant. Now I would have to check how it looks in our case. In some places on the roof we have additionally doubled up mineral wool. I think I need to have a look underneath to see if the purlin actually rests directly on the interior wall...