Is staircase DIN 18065 mandatory or not?

There is a lack of information about the upper floor regarding the house width .. upper floor = full storey or attic with what knee wall height?

Because stairs can usually be planned more space-saving and room-friendly along exterior walls when considering the house width.

And yes, your last stair measurement corresponded to the standard in terms of value, but the 23.2 cm tread depth is really not very practical. As already described here, especially when going down. Measure your foot length.

Years ago, I made 2 plans for a narrower house. The examples are only meant as inspiration now. In these, the ground floor only has a small area for the arrival of external connections, the actual technology is then located on the upper floor. The room program also does not quite match yours, but it’s only meant to convey ideas. Two full storeys were also considered here. The interior width is even only 5 m. It was for a family with 3 children.

Variant 1 could also work with a knee wall

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Variant 2 requires a full storey on the upper floor
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Our open staircase to the attic has a tread width of 230 - 260mm (depending on the step). I would never, ever have this tread width installed for the staircase from the ground floor to the upper floor. Two years ago, I had to wear an orthosis on my foot for a few weeks. Going up was fine, but going down I really had to be careful. Well, this has obviously been told to you often enough, apparently also by the architect and stair builder. In the end, you have to live with it.

Understandably, the repeated mention annoys you, but people also react to the fact that you virtually defend this stair part with various arguments, which in turn has led to criticism. Be glad, people are actively engaged with your topic! On the other hand, it can also make clear to you how fundamentally important this component is and how immensely disadvantageous it can be to overlook something or perhaps not have assessed things deeply enough. I once worked on a new build of a public building. From the huge entrance area, a 4-meter-wide staircase led to the first floor (DIN for public buildings certainly observed). Many employees did not use this staircase because it was simply too steep and the tread surface too short; there was an elevator anyway. In short: the DIN is important and regulates basic things, but there is also a very personal DIN-DNA that can make my life permanently more comfortable (this is precisely why one builds a house). So it does not give you the security that your life will then be comfortable enough. Accordingly, the DIN must be observed, but sensibly, its values can also be significantly exceeded to achieve the desired result for you. Keyword "undesired, repeated redesign": small residential units in particular require a higher degree of planning and planning skill. Exactly - I believe this will be exciting - in a positive sense!

The knee wall consists of three log planks each 17.5 cm thick... so 52.5 cm.
The upper floor extends up to the kitchen.

That looks like a 40-foot container scaled up 2.5 : 1 or reminds me of a showman's caravan with an extendable bay window. Were you Workation Globetrotter?