Basement made of WU concrete or Poroton?

In the plan of the basement, no half WW is shown.

I agree, it is all concrete, right?

I think so too, it's all concrete, right?

Yes. It is drawn as reinforced concrete. However, in the section, the wall is already masonry. Is the section part of the contract?

The shell construction company was sought by the developer after a tender and presumably the cheapest one was chosen, that is the assumption. This company either cannot provide a white tank or thinks it is not feasible in terms of time. However, I strongly suspect that it was ordered too late.

it is a general contractor.

So you have a contracting partner here who is probably more of an architect than a bricklayer and does not even perform the shell construction as their own construction service; they "bought in" the shell construction, and the respective subcontractor does not offer the dreamed price for the planned WU basement (which he would presumably have to fully purchase himself) but alternatively offers to build it himself. From a technical point of view, I would at best agree to this for the valley-side exterior wall here. What you can legally insist on, we cannot see: worst case, you have commissioned "a piece of house, looking as drawn"...

P.S.: I dislike (and it sets off alarm bells) when drawings refer to open supplements. So here it would still need to be checked how the drawing and contract conclusion relate to each other in time. Did you possibly even agree on a price without the quality of the performance already being fixed?

What you can legally insist on, we cannot see: worst case you ordered "a piece of house, looking like drawn"...

... so even worse: "take my money, and if you are gracious, then build me a house with it"???

"WU-Keller" is used by builders (mostly laypeople) as a synonym.

Here, a distinction is made between the prefabricated element construction method (concrete precast parts) which are poured on site (in-situ concrete) with WU concrete, and then there is the monolithic construction method where a formwork is created on site which is then also poured with WU concrete.

I also always discussed WU-Keller with my general contractor and later it turned out that only the element construction method according to WU guidelines was used. This has, besides the many mistakes that can be made during construction, another significant major disadvantage: a later injection sealing of leaks in the element walls is impossible because this can cause the large-area separation of the connection between the element wall and the in-situ concrete and thereby open even more water channels.
With the monolithic construction method, this is not a problem.
Therefore my advice: WU-Keller not in element construction method according to WU guidelines, but WU-Keller according to DIN in formwork construction method. If this is not contractually specified, it again creates room (financially, long-term risk) for the construction company at the expense of the builder.
I have read several scientific articles about the construction method with element walls and even saw an experiment where three core drill samples were taken and in all three it was found that the connection between in-situ concrete and element wall was defective or even insufficient. This is alarming if you rely on the sealing properties of such a construction method.
So far (again) everything in our basement is dry, but I do not expect it to stay that way for 40 years. Had I had the knowledge I do today back then, I would have insisted on the formwork construction method and if necessary tendered externally to basement specialists.

Unfortunately, savings are often made at the base of the house, as is often experienced. I do not see a black tank on a slope even in my worst nightmare, never allow that. The weather is tending to become more extreme. You are definitely investing in the basement wisely if it is constructed so that it can withstand pressing water.

"WU basement" is used by builders (mostly laypeople) as a synonym.

Here a distinction is made between the precast element construction method (concrete precast parts) which are poured on site (cast-in-place concrete) with WU concrete, and then there is the monolithic construction method where a formwork is created on site which is then also poured with WU concrete.
...
Therefore my advice: WU basement not in precast element construction according to WU guideline, but WU basement according to DIN in formwork construction. If this is not contractually stipulated, it again creates leeway (financially, long-term risk) for the construction company at the expense of the builder.

Certainly better – but my feeling tells me that the OP has already reached an important milestone if he still ends up with any WU basement with this general contractor at all.
Better precast element construction than none at all, as the motto goes...