How to realize object transfer over a distance of more than 600 km?

We built it at a total cost of roundabout 445k, we could probably sell it now for 550-600k, the remaining debt is around 380k.

You have to pay quite a lot of prepayment penalties to the bank, don't you?

You have to pay quite a lot of prepayment penalty to the bank, right?

Yes, that's what I assume too. :)
However, it can't be more than the interest debt of the first 10 years of the contract term plus negative interest, there are laws about that.
There are also calculators online where you can calculate it, at least approximately.

My cousin (allegedly) did not have to pay a prepayment penalty because she stayed with the same bank. Apartment sold, house built. However, I do not know if that was a special condition since her husband works at the bank.

You can also sell before building the new house but continue living in your house and arrange all of this in the sales contract. So moving out on day X and paying rent until then. Or a calculated deduction from the purchase price or (most of the) payment is made only on day X, etc.

Of course, nothing should be delayed by the move. And the pool of buyers is also limited by the fact that you are only allowed to move into the purchased house after one year. I think the option of building first, then selling the old house, is more clever. If you can get financing from the bank.

Yes, I assume so too. :) However, it cannot be more than the interest debt of the first 10 years of the contract term + negative interest, there are laws for that. There are also online calculators where you can calculate it, at least approximately.

If the buyer also has to finance the purchase price, he might be able to take over your loan. Then you save the prepayment penalty. Of course, this assumes that the bank would also offer the buyer a loan of the same amount.