Substrate treatment for new construction (roll) plaster

It is also simply rolled. A bit more strenuous than rolling pure paint.

okay, now I have read it correctly.. What kind of surface did you have and how did you treat it?

What kind of substrate did you have and how did you treat it?

Old gypsum plaster: not at all (there was wallpaper on it)
Old cement plaster: not at all
New drywall: primer
Noted difference: none in all variants
Gray image is currently on cement plaster, white is unpainted on gypsum plaster.

Also on Ytong/aerated concrete? I was just told to take everything from the same manufacturer, as then the products are coordinated with each other. But for me, the question of fire protection remains.

Yes, I also have Ytong. The fire protection must be applied to the Ytong (since otherwise it would "suck" the water from the plaster), then plaster, then I chose the mentioned combination (primer+textured plaster).