Painter's fleece / renovation fleece vs. textured wallpaper in new construction

Wouldn't a roll-on plaster also be an option?

When I told the drywall installer that I was planning to do that on the ceiling, his first question was whether I had learned it and do it daily...

Applying roll-on plaster nicely over a large surface. That is not easy.

Why exactly is woodchip wallpaper no longer "state of the art"? We have it in our current apartment in the living room. My parents have it throughout their entire house. What would be the concrete disadvantages?

Here in the forum, the opinion is that you should only build in a modern way. And woodchip wallpaper is currently not modern.
If you like it, go ahead.
We only have Q2 and simply painted over it, in the hallway textured plaster, because the gypsum plaster was too sensitive for me there. It's not perfect, but you don't really see much of the walls anyway.
So it really depends on your preferences and your standards.

My recommendation: have the wallpapering done and paint yourself. Then the hardest part is done by a professional and you can do the painting well yourself. That way it also works financially.

Why do you want to impose the flow method on yourselves? Apply one more layer of filler on the Q2 handed over by the construction company, then you have Q3. That is more than enough to paint afterwards. Smaller defects in the drywall panels can be easily repaired. Mold prevention is primarily achieved through the correct room climate. Almost every interior paint now contains an anti-mold substance. It is best to opt for silicate paint, as they are inherently strongly mold-resistant due to their high alkalinity.

If a layperson applies and sands Q2, they get Q2+, but certainly not Q3. If it were that simple, you wouldn't need professionals who train for 3 years and practice daily...

And it's a tough job, you shouldn't underestimate that. Then you'd really rather glue and paint textured wallpaper.

By the way, gluing fleece is not easy either. Long strips are okay, but when it comes to corners and such... you have to know how to handle it, otherwise the transition will end up looking like Q0.

And please don't buy pure silicate paint, but dispersive silicate paint. Small difference, huge effect.

Why exactly is woodchip wallpaper no longer "state of the art"?

It's just not contemporary. Smooth walls are in. Even if other generations have gotten used to their past mainstream and do not adapt to the new times, their standard is not considered the current taste of the times. This also applies to rental apartments: either it has been stuck to the wall for decades, or the landlord has his own reasons (we always had it that way). A freshly and modernly renovated apartment will rarely be equipped with woodchip wallpaper.

You develop your own taste, which is often shaped by current trends, and you go through life with open eyes and are drawn to things you would like to have for yourself, your life, home furnishings, and decor. However, of course, you can still like woodchip wallpaper nowadays and stick it in your little house.

Regarding the question: We only painted Q2. Now, after 10 years, you can see many settlement cracks. In winter or when we repaint everything, we'll fill and smooth them out, and that’s fine. Maybe next year or the year after, because such things no longer bother us. However, you talked about drywall in the upper floor, and that can really look bad. You may be pleasantly surprised, but if you don’t invest time yourself to fill the joints multiple times, you will see the seams later on. You also see every little defect the drywall has, especially in the attic with a gable window due to the slanting light coming through the window. Therefore, I would at least glue fleece or wallpaper under the sloping ceiling if you have an attic.

Overall, you can do a lot yourself: plan for 3-4 weeks. If you finish earlier, great. You can rent equipment, and for practice, you take a less important room. Possibly there is an affordable seminar at Obi or Bauhaus beforehand.