Newly built semi-detached house 155 sqm - orientation & floor plan accordingly

If you don't care about the upper floor, then that's true. But with a change on the ground floor - changing the stairs, piping for bathrooms, etc. - you also completely change a possible upper floor, even if you actually don't want to. Or you make sure that an upper floor has to get a "stupid" layout because there is no other way. Therefore, always consider all floors. It can also lead to structural issues (although rather not in a normal semi-detached house).

I understand that - but we would actually align the upper floor to the ground floor, since the ground floor is much more important to us. If it then turns out that you can't get 3 rooms and a bathroom on the upper floor, of course that's a different matter.

that we would preferably like to have a bright living space, which is why in the current plan the living room is also oriented to the south

So a dark living space in summer, because the sun shines in full force. A southern orientation used to be the holy grail. Today people are wiser and plan more intelligently. But that should be done better by the professional who knows more about it than I do. P.S. I once lived in a semi-detached house with a NNE orientation. The sun came in in the morning and during the day it was wonderfully bright thanks to the corner window. And the shading issue, because it always gets so hot in the south, was also easily resolved. Just as a thought.

So a dark living room in summer because the sun is shining in fully.

A south-facing orientation used to be the holy grail. Today, people are wiser and plan more intelligently. But it's better to let the professional do that who knows more about it than I do.

P.S. I once lived in a semi-detached house with NNE orientation. The sun came in in the morning and during the day it was wonderfully bright thanks to corner windows. And the shading issue, because it always gets so hot in the south, was also easily solved. Just a thought.

You are of course right about the shading when it comes to summer. Although we don’t quite imagine it being so dark with an awning. :) But in winter you’re happy about the sun coming in, right?

If the windows face north and east, then in our understanding there is no "bright" light after 12 o’clock – or am I seeing that wrong?

Everywhere it says that you should definitely plan the living rooms to the south or southwest and that the north is almost a cold death. That’s why we’re uncertain.

In winter, you are glad for the sun that comes in, right?

That is overrated. There is not that much sun in winter - my photovoltaic system says so too.

If the windows face north and east, then from our point of view there is no "bright" light anymore from 12 o'clock - or am I seeing this wrong?

That is relative or subjective. A semi-detached house at least has the possibility of west-facing windows. And if the living space is designed very open, additional light also comes in from the south - so a continuous axis from north to south is possible. And you can also play with window sizes. Light strips etc. There are enough possibilities. And conversely, in summer you shade the south side and just as little "bright" light comes in.

It is written everywhere that you should definitely plan the living rooms to the south or southwest and the north is practically the cold death. :) That is why we are uncertain

Yes, that is written everywhere. And everywhere it also says to please think of sufficient shading so that it does not get too warm. You have to weigh what you want, what is possible structurally, and what the property allows. In your submitted design, I would definitely prefer the right half so that I don’t get the full west sun on the house.

If the windows face north and east, then according to our understanding there is no "bright" light after 12 o'clock - or am I wrong?

Take a look at how the sun moves in winter and summer on your property – there are free and good websites available for this. From personal experience, I can say that our office and children's room, each having one window facing north and one facing east, are our permanently / year-round brightest rooms with the most pleasant light incidence, as the sun only shines in directly for a short time. This short direct sunlight also has the additional advantage that these two rooms only need the blinds for nighttime darkening all year round, since the rooms do not heat up too much even in summer and actually tend to lie in the shade when it gets really hot. Shade does not mean that the rooms then turn into dark holes, but simply that there is no direct light incidence, while still benefiting from ambient light. In our living room, which has a slightly east-south-facing window, there is direct sunlight from late morning until early afternoon.

With appropriately arranged windows or sufficiently large windows / clever window planning, rooms with a north-eastern (or east-southern) orientation can offer great living quality and excellent lighting conditions.

So we have our large eat-in kitchen on the SW side and of course large windows including a big sliding door. That is really nice in spring, autumn, and winter, but in summer you are basically just shading so that the house stays pleasantly cool. You roll up the blind once in the morning to air out and after that it stays closed all day until it gets dark again in the evening and you can air out again.
Chilling on the south terrace is also not so great, because the sun really beats down. Without an umbrella or awning, you basically bake immediately. And for that even on the street side. You have to think that through carefully. Personally, I like to have my privacy in the back of the house and don’t want to sit in the front garden.