Almost every window has scratches - what is considered normal?

Does not look good either. For now, I stick to my position: if I order new goods, I also want undamaged new goods.

The scratches from the picture on the last page can be easily polished out. Normally, windows and profiles are protected by foil during the shell construction phase and only removed completely at the very end. Of course, this can only be done from the inside; on the outside, after the window installation, not much happens anyway (with clinker bricks, the joints are still made) directly on the house.

I stick to it for now: if I order new goods, I also want undamaged new goods.

Unfortunately, the case law says otherwise. I also find it disgusting, there’s little you can do. The only way, as mentioned, is to withhold payment until perfect defect freedom, or to withdraw from the purchase contract and have it removed again. Compensation for cosmetic defects is so ridiculous that construction companies deliberately work that way (because it’s faster/more efficient) and then accept the compensation as a given.
We paid an extra 4000€ for our front door, and it was installed one day before handover. Still, it has a large scratch on the inside (happened during installation). Compensation? 0€. The scratch was polished out, but now you can see the shiny spot.
A replacement of the door is legally excluded because the defect is not proportional to the costs.
And once again, you’re the fool here because you’ve already paid a general contractor.
With individual contracts, he can watch a long time where his money goes. Small companies go bankrupt constantly for exactly this reason, because customers don’t pay.

the scratches from the picture on the last page can be easily polished out.

The window manufacturer told me the same, but I still don't trust that peace. The scratches look like that everywhere on the windows and also on the front door, where there are not only craters but proper scrapes around the fingerprint scanner. According to the manufacturer, this happened when replacing the cover around the scanner. So there is actually a notch in the plastic.

The great thing about plastic is that you can theoretically glue and fill it. Notches are obviously really annoying. The scratches are only superficial and are not a problem. Of course, the window fitter has to do that. If you don't like the result (and it really looks awful), you can still consider what to do then. For now, I wouldn't pay the full invoice amount for the windows, but withhold a reasonable amount. How much is reasonable also depends on how extensive the entire order was. Scratches and notches all over the house on all windows probably justify withholding around 1500-2000€.

We are having the house built through a construction company and I will find out what I can do about it. They want to try to improve it, but that could still take two weeks. I don't think I can withhold the money for that long, since there is still quite a bit to be done on the house. I still have a few installments to pay, depending on the construction progress. I know that polishing can work wonders on a car, but whether the window installers will make the effort to refurbish all the windows and the front door, I don't know. He only mentioned something about a cleaner they have there. They are not supposed to just clean the scratches.