What is your opinion now on the two theories mentioned in the first post? Which color type is suitable for gypsum plaster and which is not?
First of all, gypsum plaster is vapor-permeable (I wrote nonsense above). Unfortunately, you cannot apply typical especially vapor-permeable paints directly on gypsum plaster (silicate dispersion paints, silicate paint, lime paint). I cannot say anything about possible primers; the paint manufacturer should be able to provide answers.
Dispersion paint (i.e., what is sold in hardware stores as standard interior paint) can be applied to almost all substrates. They are slightly to well vapor-permeable (depends). They are available solvent-free, low-emission, and also emission-free. There is also natural resin dispersion paint (well vapor-permeable). That might be the right choice for you.
If you can live with wallpaper (woodchip or non-woven wallpaper, but not all of them are suitable, as they are often coated with plastic), then you could apply silicate dispersion paints directly. Woodchip wallpaper is vapor-permeable; it depends with non-woven wallpapers (coated or not).
Alternatively, you need to apply a mineral plaster, on which you can apply silicate paint directly.
(I also care about the indoor climate but wonder whether, if a controlled residential ventilation system is present, plaster and paint actually matter; emissions aside, of course, those should not be present).