Semi-detached house in southeast location, bright enough?

I feel the same, your worries are ABSOLUTELY unfounded

You should rather worry about proper shading (watch out, autocorrect wants to write "funeral"....). Because the south side is more window than wall. So, you don't need to worry about the brightness.

Unasked, here’s this: consider in good time whether you want a kitchen island: cooking on the island is extra expensive because of the exhaust hood, which has to be strong to handle it (strong is also expensive). Besides, in the end, you don’t spend that much time at the stove itself but rather at the sink and the prep area. I definitely recommend an island with a sink if you like working towards the room instead of against the wall. And plan space for the tall cabinets. And better avoid corners in the kitchen. So, maybe rethink the window planning in the kitchen and the kitchen planning, would be my advice.

Thank you very much for all the feedback.

Good. Then I will take a deep breath now and not worry about the brightness anymore.

We would like to stick to the island in the kitchen.
The window planning is specified by the developer. Unfortunately, we have no more leeway there. But I am confident that it will work out.

We would like to stick with the island in the kitchen.

In reality, it is much less romantic and beautiful than one imagines. Grease/heat near the passage, expensive extractor hood, little time spent there and more time with your back to the room, "sensitive" countertop if you (man) ever need more workspace than the remaining part of the island. Basically, there is no argument for cooking on the island except: I like it/I want it that way (which are usually weak arguments).

We all know it from TV. But everything there is pre-cut and the chefs don’t have to clean up. That’s why they stand cooking at the stove and the camera can film it well.
My advice remains: think carefully about why you want the cooktop there. I would find it a pity for the island and the kitchen.

In reality, it is much less romantic and beautiful than you might imagine. Fat/heat near the passage, expensive extractor hood, little time spent there and more time with your back to the room, "sensitive" work surface if you ever need more than the remaining part of the island as a workspace. Basically, there is no argument for cooking on the island except: I find it nice/I want it that way (these are usually weak arguments).

We all know how it looks on TV. But everything there is already pre-cut and the chefs don’t have to clean up. That’s why they stand cooking at the stove and the camera can film it well.
My advice remains: think carefully about why you want the cooktop there. I would think it’s a shame for the island and the kitchen.

As always, a matter of personal preference! I don’t want to give up my cooktop on the island anymore either, and in the neighboring forum there are advocates for both!
To the left of the cooktop a large area for preparation and then everything on the stove while the partner can sit at the bar with a nice glass of wine and always be there. I only need the sink briefly for washing vegetables and placing used dishes, which then find their way to the sink. Of course, the best is to have both on the island, if that’s not possible always the cooktop and never the sink!

Except in the forum, I don't know anyone who isn't a bit annoyed by the sensitive cooktop on the island. But indeed, to each their own.