Drywall with niche for mounting the shower enclosure

I would just ask.

Everything is gray here as well. Going over it twice thoroughly with Sopro or something similar should be fine. I don't think green drywall boards will help you if the sealing fails.

With the grays, however, just enough water vapor (regularly) is sufficient and the plaster deforms if it does not get enough time to "evaporate" again.

Yes. As far as I know, the reason was that a normal bathroom is not considered a wet area, according to the definition. You should also do it properly, ventilate well after showering. Better is definitely green. I don't believe it is necessary. Let's see what reports.

I made a mistake, or rather a typo...sorry. I can't change it in the title right now...as someone has already correctly pointed out, the wall is solid stone, not drywall. A back panel will be installed for the niche and then it will be tiled. Since it is solid, it is probably sufficient that the wall is not full height. That is probably the better solution anyway (lighting), even though originally I as a layman had thought otherwise. I consulted a civil engineer about it over the weekend and forced the BS. The wall is currently 10cm thick. Thanks for your detailed answers!!!

as someone already correctly pointed out, the wall is solid stone, not drywall. There will be a back panel for the niche, and then it will be tiled. Since it is solid, it is probably sufficient that the wall is not ceiling-high. That's probably the better solution anyway (light),

The aerated concrete wall will be clad with drywall (green), which is (also) the "back panel" of the niche.