The floor plan proves to be poor during the shell construction

What kind of inflexible general contractor is that? It's only about a window - that doesn't mean the construction has to be stopped.

That's what I think too. How much has been built already? Talk to the general contractor, complain... you can have a mason install a wide patio door in the south. Now, not later. Later creates too much dust and is even more uneconomical. The garage can be moved a bit further forward. Is the entire shell already standing?

First of all, stay calm, sleep on it, everything will be fine. The house is definitely not completely ruined just because a few decisions were suboptimal. They say - the first house is built for an enemy, the second for a friend, the third for yourself. We have now reached the friend stage. ;)

We also stood in the shell construction today and thought "OH man, it’s so dark in this place," but that will get better. We are building for the second time and somehow everything normalizes. The lighting conditions, and also the sometimes bizarre room sizes in the shell construction.
Walking around on the foundation slab thinking "there’s no way this is X square meters" is a very traditional experience for home builders. :)

Yes, that’s exactly how it all feels. Windows too small. Walls too many. Rooms too small and you whine. For one window size, I also let myself be talked into believing that smaller was better because it’s right next to the shower. But the same size as the window below and frosted glass would have looked much better. The windows occupied me for a long time, but now I realize that it wasn’t planned optimally. The only input from the site manager was the reduction of the windows. I thought he would know what he was doing, but now I regret not being more persistent.

And even if no window goes in there now, there's the couch anyway. And towards the south/west, we often have the blinds down so that you’re not blinded when watching TV or reading. And if you really want sun, then go out on the terrace and enjoy the sun until evening. That’s no reason to be sad. You built a house with KFW funding and low interest rates at the latest possible time, which probably wouldn’t be possible now. Then you have a nice floor plan. And the perfect plot simply doesn’t exist. So keep your chin up! It’ll be fine. And between October and March, the sun is probably so low that you won’t get any light through the large apartment building anymore.

I think so too. How much has already been built? Talk to the general contractor, complain… you can have a mason in the south install a wide patio door. Now, not later. Later creates too much dust and is even less economical.
The garage can be moved a bit further forward.

Is the entire shell already standing?

The shell is up. But I have been discussing for over a month now (back then the windows were not even there). First I had to persuade my husband, but the site manager is persistent and does not want to change anything without a construction stoppage.

And even if no window goes in there now, there’s the couch anyway. And towards the south/west, we often have the blinds down anyway so that watching TV and reading isn’t blinding. And if you want real sun, then go to the terrace and enjoy the sun until evening. That’s no reason to be sad. You built a house at the latest possible time with KfW and low interest rates, which probably wouldn’t be possible now. Then you have a nice floor plan. And the perfect plot simply doesn’t exist. So keep your chin up! It will be fine. And between October and March, the sun is probably so low anyway that you won’t get any light through the large apartment building.

The sun until the evening only works in the front yard. That was also a long discussion. I wanted the living room facing the street side so that there would be a second terrace there, but my husband didn’t want a living room in the front. Yes, if we started now, the interest rates would be twice as high monthly and we wouldn’t have the KfW subsidy either. If additional windows are installed at some point, the costs are not even as high as the subsidy (according to my husband who is trying to calm me down).

And believe me, the feeling when you move from your shell construction into a house with your self-chosen floors/tiles is an incomparable feeling and you will feel comfortable right away. And a terrace facing the street would not be my thing at all, after all, you are sitting on display. Be happy about what you will have soon. You can always optimize later and installing a large terrace door can't possibly cost the earth (even in 3-4 years).