Waterproof basement - "Fresh concrete composite film"

That fits according to the guidelines:

Walls, exposure class 1 (in-situ concrete): 240mm
Floor slab, exposure class 1 (in-situ concrete): 250mm

The statement unfortunately seems poorly substantiated... sorry to say it like that. But then the next user here in the forum can come along, claim the exact opposite, and it cancels out.
For example, me: It is indeed the case.

A few references are always nice in such cases (no links, as they are forbidden)
- Building physics studies from TU-Berlin
- Information sheets from Informationszentrum Beton GmbH in Erkrath
- Publications of the German Committee for Reinforced Concrete

are just three of many sources that confirm this.

Especially your last source says exactly the opposite. From a component thickness of 20 cm, no moisture transport takes place anymore.

Oops, there was still a comment on the quote. All the better!

Here is the source reference anyway:
Excerpt from "Cement Data Sheet Structural Engineering H10 3.2012 - Watertight Concrete Structures" published by InformationsZentrum Beton GmbH. Authors Dipl.-Ing Thomas Bose, Dipl-Ing Rolf Kampen, and generally InformationsZentrum Beton.

Hm, once again about diffusion:

Thank you for this hint! So do I understand correctly that with a thickness of 24 cm, a maximum capillary and drying range of 8 cm leaves a core area of 8 cm again?

Now I am really at a loss. The logic immediately demands the decision for the WU basement!
Because if already at 20 cm wall thickness (almost) no overlap of the capillary and drying range occurs, then with 24 cm you are really on the safe side.

Phew, yes....I think the decision is clear then. I would rather invest the 3000 euros in perimeter insulation.

Exactly the source I meant. It states, among other things, "In WU structures, diffusion in the drying area slows down over time and practically comes to a halt after the moisture has been released [5], [12]. Also, in [14], no cases of increased humidity were reported under constantly pressing water (floating houses)."

Now only one problem remains for me:

The exterior walls are constructed with a double shell and filled with cast-in-place concrete.
What material are the formworks made of then, hopefully also made of [WU-Beton]?