Does the municipality want to purchase shares of my land?!

No matter how high the investments are, he only becomes the owner after registration, and that definitely has not happened after 2 weeks.

Then I hope you don’t need an appointment with a lawyer afterwards. If the notary is actually at fault, maybe he can make up for it in the now still necessary negotiations with the municipality.

I hope so too, thanks for your assessment! I got an appointment with him tomorrow, so hopefully everything will be clarified then.

As I said, I had agreed with the seller that first a pre-registration of conveyance (reservation) would be entered for me in the land register (to be sure that everything is correct here). Afterwards, that is after release by the notary, the first installment (50% of the purchase price) becomes due and I can start renovating the upper floor as well as use the garages for my purposes. The seller will have completely moved out by the end of October, then the handover and payment of the second installment will take place as soon as I am registered as the owner in the land register (again release from the notary, then payment of the second installment = 50% of the purchase price).

I discussed this procedure with the notary beforehand, he saw no problems in it.

Well, now I probably do have one...

The notary will surely argue that it is merely his task, until full payment and registration in the land register, to ensure that he informs me if someone exercises their pre-emption right.

For my part, I assumed that a "release for payment of the first installment" was synonymous with a "release for renovation and moving in." At least, that’s how it was conveyed to me in conversation. As a layman, I am not familiar with the applicable laws here and I relied on the statements of the notary.

How high are the investments already made in the house?

They are still kept within reasonable limits; so far, I have bought about 8,000 euros worth of materials and spent about 1,000 euros on craftsmen.

The notary will surely argue that it is merely his task, until full payment and registration in the land register, to ensure that he informs me if someone exercises their right of first refusal.

If he has sent you written approval for payment, even if only for the first part of the purchase price, he thereby confirms that all criteria for the transfer of ownership (except for the payment) have been met. This also includes checking for building encumbrances, priority notices of conveyance, entries of land charges, and examination of possible rights of first refusal by third parties (usually municipalities, the federal government, or states). This is what our notary said during the house purchase. At that time, he also specifically pointed out that we should not pay the purchase price until we receive a payment request from him, as otherwise he cannot guarantee that all requirements are fulfilled.

This is certainly regulated by law. It is best to first try to talk to the notary and refer to his letter (which hopefully is called a payment request and not a "paper for green light").

If he has sent you the payment release in writing, even if only for the first part of the purchase price, he thereby confirms that all criteria for the transfer of ownership (except for the payment) have been met.

I have received such a letter with the subject "Notification of the occurrence of the conditions for the maturity of the 1st purchase price installment." It also explicitly points out that all the necessary conditions for the transfer of the first installment have been met; additionally, an excerpt from the land register or a copy of the registration announcement for the priority notice of conveyance has been attached.

As a prerequisite for the payment of the first installment, freedom from pre-emption rights, land charges, priority notices of conveyance, and encumbrances on the property to be sold is already noted in the purchase contract.

I agree with Till. In short: before you pay, it must be clear that everything is kosher. This also includes the right of first refusal. But I suspect the notary will be able to point out that it took too long with the municipality. We'll see.....

But I suspect the notary will be able to intervene because it took too long at the municipality.

But only as a hypocritical excuse. He should have applied for a negative certificate, and if that does not come immediately, he must either inquire where it is or wait for the notice regarding the exercise of the right of first refusal.