TV show about the tricks in construction...

The bitumen layer is intended to prevent diffusion and, according to the manufacturer and standards, must be installed compulsorily. That some skip it does happen, one just has to know whether the risk is worth it. We have deliberately commissioned and inspected it.

Ok with an open basement that is still going to be plastered, I can understand that. In the case of a in-situ concrete basement where the soil puts pressure on the perimeter insulation, your variant is established practice and according to my offer saves about 3k gross. Even without glued insulation, no water gets through :) Now the question is whether you paid the 3k€ and it was not executed or if it was "credited" to you because it was not executed.

That was the classic case where I read the offer but didn’t understand everything and relied on the site management who supposedly had done this 100 times before. The layer wasn’t included in the offer, was executed accordingly, and therefore not paid for ... but since the basement protrudes to the north, I would have liked it .... I just wanted to make it clear that maybe experts should be involved earlier, namely when obtaining offers for the major trades.

No water comes through even without glued insulation

Insulation always needs to be glued, including in the perimeter area.
If it is penetrated by water, its effectiveness is significantly weakened.

Since this is currently about the broadcast on NDR and also floor slab insulation, I would like to recommend the NDR contribution.

I have only dealt with the topic of floor slab insulation energetically a little, but the two negative examples in the film show that even after 4 years, a poorly insulated?/insulated floor slab can cause moisture in the house.

Perhaps someone can explain more to me about the causes of the mentioned "water damage" and how these can be prevented with advance planning.

Such a house is founded on a waterproof, continuous concrete slab.... moreover, the construction method depends on the load case, one could possibly consider a drainage system to divert the water. That no water gets in then has to do with the sealing but not necessarily with whether it is insulated or not