Cladding in floor construction at the staircase

I need advice on the best way to do the floor construction at the staircase because there is no wall. Later, a wooden railing will be installed there and the side surface of the floor construction will be clad with wood.

Don't quite understand the question.
[Screed] -> [Railing] -> [Flooring]?
Or what exactly do you want to know?

The insulation, underfloor heating, and screed must be in contact somewhere, otherwise the screed will flow away. However, in the end, when the screed is solid, everything should run in a straight line. That is, from the end of the plaster to the floor construction which is to be clad on the side with wood.

If I had said "back then": "find the mistake"

The architect is planning our house until the approval.

... a whole bunch of (readers) wouldn’t have understood that again.

Don’t quite understand the question.
Screed -> railing -> flooring?
Or what exactly do you want to know?

He probably means: at the transition of rising stair-accompanying walls to the floor – at the collarless stairwell – you will now look directly at the bare structure of the floor build-up. Now a covering of the mishap is being sought.

If you didn’t "dismiss" the architect after service phase 4, you’d have someone who should have already drawn the answer. But as a proboscidean, you can trumpet that against the wall, no one gets it.

The insulation, underfloor heating, and the screed all have to adjoin somewhere, otherwise the screed will run away. Only in the end, when the screed is solid, everything should run in one line. So from the end of the plaster to the floor build-up which is to be clad with wood on the side.

Nope, if it’s only about the screed not running off the edge – you “form” that with a simple plasterboard.

Floor slab, formwork, what else? Who is responsible for that? Clad any "bare" surfaces with wood, tiles, plaster, or whatever. I still don't quite understand the problem...

For example, you can put wood or plaster on it. I will have wood installed by the stair builder. But I am still not sure how it will look finished, since I have a 20 cm structure in the upper floor. I am worried that it might be too much.