Bright lines on fresh interior plaster - future cracks?

I can confirm the statement by von guckuck2 from extensive practical experience. Of course, dry cold air is good, but cold air also absorbs much less water than warm air. Therefore, regular air exchange is important. The walls then warm the cold dry air, and it then absorbs the water again. When we have unheated objects, drying always takes forever. The cracks in the corners of the windows are often normal if nothing is done against them, like a diagonal reinforcement.

Now you'll surely explain to us where the moisture goes when windows are closed with the heat sources on?
So the house is basically airtight sealed with various vapor barriers, triple-glazed thermal insulation windows, or the ETICS external insulation.

Not much goes out during shock ventilation.

Because of statements like these, people have mold in their homes.

You are completely wrong. You do exactly as I said. You perform shock ventilation multiple times daily. If you want to automate it or make it more efficient, you can also use construction dryers.

Cold air is dry but can hardly absorb moisture. Warmed-up air can do that very well. Moreover, not much comes out from cold components, especially not with a 6 cm thick screed. What you want to do is dry the surface by drafts. That works too, but that is not the task here and DAMAGES plaster and screed.

Your theory works in drying shell constructions. If you do that with plaster or screed, you damage them. It's that simple. Feel free to do it yourself if you want, but as a recommendation in a public forum, it is absolutely unsuitable and cannot be left like that.

Everyone just has their own opinions. I find it a bit sloppy, at least, when no mesh is integrated around the windows. And if plaster and screed are applied together, then there is definitely too much moisture in the building. But everything has to be done quickly anyway. No one should be surprised if the drywall molds.

Everyone has their own views.

No, that's physics. No one said the windows can always stay closed when heating. Regular ventilation is, of course, necessary. Exactly what says is correct.

I find it somewhat sloppy when no mesh is integrated around the windows. And if plaster and screed are applied together, then there is definitely too much moisture in the building. But everything has to be done in a hurry. Nobody should be surprised if the drywall develops mold.

Here I fully agree with you.