Financing detached single-family house (new construction)

But that's also a pretty nasty interest rate. It has been significantly better before.

and it has also been significantly worse before. And now?

Something has changed in the meantime. We now have a full repayment loan at (in my opinion) not so bad conditions.

400,000 EUR as an annuity loan (1.9% nominal interest rate, 30 years fixed interest period, 3x amortization rate adjustment, 5% special repayment)
200,000 EUR as a building savings contract (1.3% nominal interest rate for pre-financing - fixed interest period until allocation - and after about 10 years 2.15% nominal interest rate for the 10-year construction financing)

If you want to afford the 30-year fixed interest period, then it really looks good.