Staircase shifted by 10 cm, options?

I don't understand that: especially if he had measured on site, the result should rather match reality than the plan (???)

The staircase fits the stairwell (thus reality), not the plan. The planned staircase probably never fit the planned stairwell, because otherwise the metal construction would have ended in mid-air.

Yes, that would be my preferred solution. That’s why I’m asking if the stairwell can be reduced in size.

I think as a layperson, but with some sense: probably not, since everything somehow segmented doesn’t support much. It’s no coincidence that they say the staircase comes first and then everything else adapts to it. Or can you somehow work with beams in the basement that then support the small extension?

I don’t see the trip hazard either, I’m concerned about going down the stairs.

So the 95 instead of 104? Cm?! I’d say this: with 95 you can easily push yourself off the outer wall if you’re going too fast?! :p Otherwise, you have to acknowledge that Kerstin pointed out the bottleneck to you. Luckily it’s open, so you can get furniture upstairs. Complicated but possible option: widen the window next to the front door and install a bay window that projects outward.

So, from what I would read here, the stairwell was executed larger than planned. The stair builder was then instructed to orient himself not by the plan, but by the actual stairwell. Based on these measurements, he built the stairs, and this results in the "deviation" at the top, the 10 cm narrower passage, AND the overhang at the wall. Because to get everything flush with the wall, the support surface is probably simply missing. The stair builder is hardly to blame with this instruction, as the whole thing is caused by the incorrectly executed stairwell. Whether this can still be "repaired," the stair builder would have to say. Whether it would be possible to push the stairs further into the stairwell with a modified support at the bottom. But the contact person would be the general contractor, as the stair builder probably executed according to the instructions (though not according to the plan).

The staircase fits the stairwell (thus reality), not the plan. The planned staircase apparently never fit the planned stairwell, otherwise the metal construction would have ended in mid-air.

Do you enjoy joking with us like Chris Howland or Kurt Felix once did – where is the hidden camera? Now you even say – although your photos are not really convincing for that – that the element AND its hole would actually fit together, so where exactly is the problem? – is it perhaps the stairwell that is 11 cm too far "forward"???

Do you like joking with us

I love joking for my life ;-) but I think there is simply a misunderstanding here.
My statement is: The staircase fits the stairwell. This is correct in the sense that nothing is hanging in the air, you can walk on the stairs, and you don’t fall into a hole anywhere.
Nevertheless, I also say that the distance to the wall does not fit. Whether this is due to the stairwell or the staircase design is beyond my knowledge.

If it is due to the stairwell, then the planning is wrong.
If it is due to the staircase, then I wouldn’t know how the staircase should have been designed differently. This doesn’t have to mean anything, as I have no idea about staircase construction.
Maybe the metal construction doesn’t have to rest on the underlying ceiling at all but can be attached differently. I don’t know.

If it’s because of the stairs, then I wouldn’t know how the stairs could have been built differently. This doesn’t have to mean anything, since I have no idea about stair construction. Maybe the metal structure doesn’t have to rest on the ceiling below at all, but can be fastened differently. I don’t know.

I am not a stair builder either, but the construction is certainly possible in several connection variants – this is known from garage doors with different order dimensions depending on installation behind or within the reveal, with otherwise the same rough opening measurement. Sometimes a little talking past each other is enough that the finished piece has to be installed “the other way around.” What exactly is your issue: to go a bit slimmer past it at the bottom (i.e., unfortunately not being able to put some decorative clutter in the way) or to always do the last step like the butler from “Dinner for One” on top?