Is a soil report not possible before surveying the new construction area?

In our soil survey, exactly the points of the house were measured and drilled where the most load will later come down (I don't know if it's a coincidence, but for us these were the corner points of the house). You can already take some chances somewhere, but I would wait until you know where the house will be located; only then does the structural engineer have planning security...

Often, the municipality conducts a rough soil survey for the entire building area before development; you should inquire there. At least it roughly states what the soil is like, and you can at least estimate whether there will be a landfill after 30cm or not! More precise data will only be available once measurements and drilling can be done...

I have a question about that as well.... In our new development area, there is such a comprehensive soil survey.... a drilling was even carried out on our property with the result that it is clay... Our construction supervisor said we do not need a soil survey. We are building with a white tank / concrete cellar. Should I still have one done?

No. You have everything the civil engineer needs. What further insight is that supposed to bring?

I thought something about groundwater or possibly that the soil needs to be replaced, but I am not familiar with it

That would be in the provided [mitgelieferten].

If in principle only one borehole somewhere on the property would be necessary, I wonder why several boreholes are always made and precisely surveyed...

Often, the reports from the municipality are not that detailed either...

With a bit of courage to tolerate gaps, I think that an additional geotechnical report is only recommended if you are building a correspondingly statically "demanding" house or if the boreholes from the municipality within the entire building area have shown that the soil conditions are very different... You always have to see this somewhat in relation to the house...

Friends of ours built on a very steep slope and had 3 boreholes made. The only problem was that exactly between the boreholes a rather large peat field was discovered, which was not detected in the geotechnical report... That then caused a staggering additional cost of €15,000. I learned from that that even with the most detailed geotechnical report, you are not safe.