Preliminary insolvency of the developer - What to do?

Yes, that is true, but on the one hand, one is advised to definitely go to a lawyer with it, and on the other hand, it doesn't help anyway. I am now investing the money and see if we get back 1-2%

Good luck! Did you still receive the last paid items?

No, the work plan is still open as well as the statics and the electrical plan. Overall, this is sh ....

Actually, almost all builders who are really in deep trouble have overpaid for their construction.

Yes, that's true, but on the one hand, you're advised to definitely go to a lawyer, and on the other hand, it doesn't really help. I'm investing the money now and see if we get back 1-2%

a lawyer for the whole matter costs (assumption) €1000 and nerves and at best brings back €1000. The question in the end is whether it’s even worth it. It might be better to first contact the insolvency administrator yourself and ask if any work will be continued. If the administrator is only supposed to catch the coup de grace, there won’t be much to gain anyway. As a customer, you’re the last to get anything.
What I find awful is that the sellers tricked you into this. They knew that nothing would come of it, and yet they knowingly dragged you into it. I’m always surprised that they get away with that (also informally through personal meetings). There are cultural mindsets in Germany that have no tolerance for such things.

Final info: The insolvency proceedings were opened on 01.06.2017. Debts amount to approx. 1.5 million. The insolvency administrator has calculated a quota of approx. 10%, so a small portion may possibly be returned.