Legal question regarding the plot of land and the bank's handling

That depends on the bank's caseworker. A knowledgeable and conscientious employee does not adhere to the usage types in the land register.

Wait a minute, if building land was priced in before, but now part of it is only recreational area (how much exactly), then something inevitably has to change because possibly only one house instead of three can be built. That significantly lowers the value. And a conscientious bank employee is supposed to just accept that?

if building land was priced in beforehand

How did this pricing come about? The bank should have conducted a valuation before granting the loan. If this was done at the desk only on the basis of the land register excerpt, that is unprofessional. One must be convinced of the accuracy and also take into account the planned possibilities or restrictions of use.

because maybe only one house instead of three can still be built.

However, this does not depend on the actual use in the land registry/cadastre, but on the currently applicable planning law.

One must convince oneself of the correctness and also take into account the planned possibilities or restrictions of use.

As I see it, the possibilities of use have changed, or do not correspond to the expectations of full building land agreed with the bank. More details and facts could help.

Previously forest, garden, and recreational area (3 parcels). Now completely recreational area (1 parcel) (building permit for a single-family house is available). Since the land register excerpt was initially not updated (error at the authority, resolved by the cadastral office), the bank had questions. However, this has been clarified. The bank approved the loan because they apparently also saw that the questions were strange given the existing building permit.
In any case, building in the second row is not conceivable from a planning perspective, since along the entire street this has not been done, but basically in a single line. Our house will stand on all three old parts of the parcel.
Nevertheless, it is of course correct that I did not value the property, but the bank did, and I could only present that building is allowed on the property as stated in the permit.
Since the cadastral office only makes the entry for the building area after the building has been surveyed, I wonder if this could theoretically still lead to problems with the bank. The bank told me that when the time comes, I can simply submit the new excerpt.
The bank is a reputable, very well-known bank.

This has been clarified, however.

Your second post is from Friday 21:54. What could still have been clarified then? What exactly is your problem now? You have an approved loan and an approved building permit – let's get started.

I wonder whether this could theoretically still lead to problems with the bank.

Are there any questions left open?