Freestanding bathroom wall: Does the wall hold a double washbasin?

11ant thinks that the wall should not have any contact with the ceiling, but should simply end after about 2m or 2.2m.

I think that is clear to everyone. The question is still what kind of ceiling is under the screed?

What is the ceiling made of? Concrete with steel or wood?

Regardless:

Will the wall hold if you hang a double washbasin on it later?

I had planned to build it with aerated concrete, 17.5 cm thick

That will be difficult; especially because you still need to weaken the wall to accommodate the piping inside it (especially the waste pipe).

The best option will actually be Geberit GIS. However, your desired size does not quite fit within the manufacturer's specified limits.

Below is a reinforced concrete slab (C30/37) 20cm thick.

Currently, I plan to subsequently install the connection reinforcement for the wall and cast concrete supports in the wall.

Procedure as follows:
1. Drill holes D12mm
2. Clean the drillings
3. Fill in injection mortar
4. Insert reinforcement bars D10
(For each support, I wanted to glue in 4-6 bars - half of them on the outer sides of the wall.)
5. Then build up the wall to the planned height of the bracing supports (1 - 1.5m). Two recesses will be provided in which the bars run or the concrete must be filled.
6. Formwork and concrete.
7. After drying, complete the wall to the planned height

It is also important that the masonry is interlocked accordingly so that the concreted supports provide good stability to the wall.

I hope my plan succeeds

Why don't you put some masonry supports in front that can hold a slab, in which the sinks can be recessed or placed on top. You can also mortar a small plinth on which a base cabinet can stand. With this idea, you kill two birds with one stone: stability as well as a nice washing area.

I believe that is clear to everyone. The question still is what kind of ceiling is under the screed?

To make it really clear to everyone, apokolok differentiated this in #8 and called the lower ceiling "floor". In my opinion, the subsequent question about the ceiling logically refers to the bathroom ceiling, not the floor below. Hence my note that no anchoring is planned upwards.