Bathroom ceiling moisture + inadequate insulation

We have had a new bathroom on the upper floor for about 12 months. That is the only room where I have not documented the renovation work completely and without gaps. So far, fortunately, nothing of that kind has occurred. I will assume that we are spared this and hope for the OP that I have handled the matter favorably!

I hope that the whole process of letting it dry and then insulating is really done. We will definitely have access to the attic made so that we can check regularly in the future. During the construction phase, we thought we didn’t need that yet... well, now it would have been helpful.

Does anyone have any idea how the moisture could have gotten between the drywall and the foil?
Could it actually come through the ceiling spotlights? Or through the joints between the wall and ceiling (sealed with acrylic, but torn in a few places due to the house’s movement)?
The moisture definitely did not come from above, the foil was only wet from below.
I’m worried that if we seal the ceiling now, in 2 months we’ll have the same problem again.

As far as I know, Rigips does not provide any real resistance to water vapor. Should excessive moisture not be excluded by the controlled residential ventilation?

But the green panels are specifically for wet rooms... We do not have [Kontrollierte-Wohnraumlüftung]

Yes, the green boards are for wet rooms. However, this does not mean that they are impermeable to water (vapor).

Ok, I understand. But that would mean that my (first) problem with the moisture between the board and the foil should occur quite frequently, right? ?