Basement permanently sealed?

What does high groundwater mean? If it is already at the level of the basement walls now, it will get wet.

And is that the gravel from the concrete? Where is then the concrete :-) oh dear.

Not quite level with the basement walls, but still.
And yes! That is the gravel from the concrete.

The black coating is supposed to be waterproof now. However, I am very uncertain now.

Where can you find a proper expert?

Inquire, for example, with [Bauherren-Schutzbund]

Furthermore, there is the Federal Association of German Building Experts

Today our concrete slab was poured. On this occasion, I asked an employee how what you described happens and what the solution is. He told me these are gravel nests that occur when the concrete was not properly compacted, and you can only seal them reliably with a certain synthetic resin that is pressed into the joints from the inside with high pressure. The price is supposed to be around €20,000. But this is second-hand information.