Loan agreement for only one person: advantages / disadvantages

Not on the house, because it is not registered in the land register. But possibly on a compensation payment.

No, not on the house, but simplified it is on half of the repayment made during the years of marriage. I am not a lawyer and in practice I believe it is significantly more complex, but that is roughly how it is.

I repay completely on my own, but would she still have a claim without ever having paid a cent for it?

Basically: Yes!

But it is very difficult to generalize if it is not clearly separated throughout the entire time who paid what and how. However, if not clearly regulated otherwise beforehand, the spouse is definitely entitled to a value equalization, since you are jointly assessed during this time and thus the repayment of the loan comes from your joint account. From which account it is debited is not decisive.

If this is not desired: prenuptial agreement

I am paying it off completely on my own, would she still have a claim without ever having paid a cent for it?

With 2 small children, she may have the right to live there, if the court decides so, even though it is your house, which you are paying for.

At least, that was the common practice... but it is also possible that something has changed by now regarding the decision-makers, so that today a different decision is made

I actually built it alone on purpose so that after a divorce the whole thing wouldn't be so complicated and one partner wouldn't have to pay out the other or they wouldn't fight over the house. Well, whatever, there's no way around a prenuptial agreement because I definitely won't let my house be taken away from me.