Stair railing with drywall

No problem, I have attached it.

I looked at the whole thing again on site and the staircase is 111cm wide (edge of stair step to plaster). Theoretically, I could also use the 75mm profile, since 100cm is okay for a staircase. The question is whether it is necessary. Actually, the staircase should be 10cm wider and 2.5cm can be a lot when carrying a couch.

But I believe the drywall solution is completely sufficient. I always had the image of a classic railing, where the posts stand every 60-100cm. I also had the concern that the dowels of the UW profile would not hold. But these are all wrong assumptions. The UW profile is only there so that you can fasten the panel at the bottom. The stability comes from the UA profile, which is mounted on the side of EACH stair step. Thus, I have a UA profile every 26cm and if I fasten it with 2 dowels, the leverage is no longer so extreme. The UA profiles are then connected with gypsum fiber boards, so the force will also be transferred to the other UA profiles.

That should be stable. Before I start, I will first mount one profile and see how stable it is.

What do you think?

If an experienced (?) shell builder wouldn’t go below 12.5 cm to get a sufficiently large surface connection, I would have serious concerns about a point-connected, free-standing drywall.

The railing also has a function when you need to hold on to avoid a fall, for example. If 100 kg acts on the lower profile with a lever arm of 1 m...
The wall itself will be stable, but with the one-sided connection, that seems too adventurous to me.
Then it’s better to leave it out altogether, so no one gets the idea to hold on to anything.

If I remember railings correctly, they are primarily (all?) connected sideways at the end face, most likely because of the edge distance of the anchors.
I would do the same in your case and also use steel profiles.
Attach the profiles with proper anchors at the end face; attach a wooden battens to the steel profiles and then screw the drywall panels to them.
If you don’t have space to build sideways, you could also slot the stair treads sideways and recess the profiles accordingly.

If an experienced (?) shell constructor wouldn’t go below 12.5 cm to get a sufficiently large surface connection, I would have serious concerns about a point-supported, free-standing drywall.

Hm, I find the comparison difficult because one has nothing to do with the other. A free-standing masonry wall can almost always be knocked over because the wall is only superficially connected. I want to screw the UA profile to the staircase.

That should be stable. Before I start, I will first install a profile and see how stable it is.

What do you think?

I have the feeling that you are already so focused on the drywall that you don’t want to hear anything else anyway...

A single profile as a test probably won’t be very convincing, since it is the cladding that provides the necessary stability.
My opinion on this....

Yes, we would like to solve this with a drywall partition, as we can't think of any other option to achieve as thin a wall as possible. Of course, we are open to other suggestions, but we don’t dismiss our idea immediately just because someone "believes" it wouldn’t work. This is not meant as criticism, as the answers here have provided some food for thought.

An alternative would be, for example, a post holder like in the attachments. The first variant would be more stable, but I would have the problem that the flange would be visible from the side. The second post would be better in that regard. Here, you could insert a wooden post and attach the panels to it. But is this more stable than with the UA profiles?

Of course, the cladding provides additional stability, but if the concrete with a UA profile chips off under slight pressure, I wouldn’t do it. However, if that already seems stable, then it should only get better with the cladding. That’s what I meant.

As I said, I am open to other implementation suggestions. We would like something like attached

What you want to alternatively execute in drywall is the masonry shown with d=6cm? - that would be 14 cm including the intermediate space if both sides are implemented in one element. The geometry of the construction will then need the rest of the Christmas holidays to be drawn and in my opinion it is probably also advisable to switch to a squared-timber substructure, but on the other hand, this significantly stabilizes the whole thing. The reality is different from the example image, because in your case this construction practically grows out of the wall around the storage room under the stairs.