Building on still foreign land - Waiting for building permit

That is correct, the leaseholder is at no time the owner in the land register. Since this part of the internet doesn't recognize links, you had to google.

Huh? I am in the land register and have a ground lease. And the house will no longer belong to the lessor. Unless I sell it to him. I have it in black and white.

That is so, the leaseholder has never at any time been the owner in the land register. Since this part of the internet does not know links, you had to google.

googled: The ground lease contract apparently is indeed in the land register. When it expires, the house reverts to the owner (reversion). However, compensation must be paid. It amounts to at least 2/3 of the value.

Didn’t it say something about [Auflassungsvormerkung] up there? We haven't had anything else for two years and have already moved in by now. Both the notary and my lawyer had no concerns. However, we paid immediately. This reservation practically secures your place in the land register and there is no way back for either party anymore.

willo, that's how it is.

This preliminary note practically reserves your place in the land register and there is no way back for either party.

However, our contract includes a right of withdrawal. This means that if we were to withdraw, for example, the real estate transfer tax already paid would be refunded.
The seller, however, cannot withdraw.

He just doesn't want to be liable for nothing

As long as he is the owner, he is liable. If it snows and it is not cleared and someone is injured, the owner is responsible.

when felled trees fall on a parked car

Then the person who caused the damage is liable. If an obviously sick tree falls due to storm, the owner is responsible again.

For example, you simply lack the right due to lack of possession. I want to see the building authority's reaction to the construction start notification

The building authority does not care about that. If owner involvement was considered necessary at all, it already took place during the approval process.

Everything you would build there belongs to the current owner.

That is correct. In leasehold contracts, clauses should exist regarding how to handle the building stock after expiration (everything from repurchase to demolition is possible).

So from the bank's side, it should be no problem.

However, the seller cannot withdraw.

Then go ahead and start.