Building ground suddenly a biotope

Because the city only sold it together. [...] So our developer offers it with and without land, so we signed with them, they told us the fixed price and then it is built turnkey without us having to do anything.

There are companies that act both as general contractors (land belongs to the client) and as developers ("client" buys house / house construction with land). To whom was the land sold - to you or to your turnkey builder?

In any case, the construction pit is almost always in the biotope except when we build completely by the street.

What kind of super-duper ultra-holy biotope is that if you are not even allowed to touch it for a slope that will be renatured afterward?

We have bought the property. It is called Magerwiesen but it looks like any other meadow. According to the developer, sheet piles or something similar are still possible but cost around 50,000 euros. That’s why we hoped there is a law that no biotope may be placed on an existing building plot.

It's called "Magerwiese" but it looks like any other meadow.

I just created one on my property with a lot of effort. Very valuable for insects and crawling creatures. Be happy - you have it right there.

Would you give the property back if you had to build differently? What do you want to achieve? A price reduction or cost reimbursement? I think you won't get any further without a specialist lawyer.

We bought the plot of land.
It’s called Magerwiese but looks like any other meadow. According to the "builder", sheet pile walls or similar are still possible.

If it is your plot, the "builder" is a general contractor. A Magerwiese (poor meadow) is not that special after all. In your place, I would ask the district office / district administration authority whether they would approve a violation of the biotope on the condition that the affected area is renatured after backfilling the excavation slope.

That’s why we hoped there is a law that no biotope may be placed on an existing building plot.

Landscape protection does not provide for direct citizen participation, and consequently no right of objection for affected landowners, who are also not individually notified about the establishment of the protected area. So your plot has very likely been lawfully affected in this way. However, I do not see any damage here, provided a practicable building window remains. If you are now upset that large intended windows coincide with the front edge of the building window, that will not change anything, and redesign costs are your pleasure.

The problem is
1 it is next to the parental home
2. Property prices have exploded here
3. There are currently no more that are affordable
4. We have the old prices from the developer and would then have to make a new contract which would then be significantly more expensive.
What I hoped is that someone knows a loophole.

In this building area, we would still have to intervene in the biotope. We have already sent this request to the district office but have not received any feedback from them as it has been under review for about 4 months.