Is the land use plan binding? Possibly a building window in forest area?!

Our little house is also located on former land designated for future agricultural use in the outer area. :) (no longer nowadays) At that time, we made a purchase contract with the owner, where the positive preliminary building inquiry was a condition for the actual purchase. Before that, we also talked a lot with the authorities in the small town and promoted our project. We had some support from the community, which was certainly not unimportant in the final decision of the building authority.

Thanks so far to everyone!!

maybe I was a bit unclear. According to the information we have, there is no development plan there and because of a few small gaps in construction, none is planned. Since it should not be an outdoor area due to the location (I will find out for sure at the building authority), paragraph 34 probably applies. We are now a bit scared because of the overgrown condition together with the "actual use". Therefore, we had hoped that the land use plan is binding and that we are allowed to build at least in this red area at the back. Given the size of the property, that would probably be okay for us. Ideally, it would of course be better to build directly at the front...

But apparently only the building authority can clarify that...

Has anyone had experience with such "vague" preliminary building enquiries? That is, without a sketch, building plan, etc. The only thing being the development itself?

We initially also tried to submit only a simplified preliminary building inquiry. It was sent back immediately with the reason that it was incomplete and only by the expert, etc.

Now our question is, how binding is this for the building authority?

The land use plan is the preparatory land-use plan (see Building Code, Section 2), the development plan is the binding land-use plan (see Building Code, Section 3). Without a development plan there is no binding planning law.

However, the attached picture clearly shows that a part of the designated parcel is intended as a building area in the land use plan

From the picture it is clearly visible that this is not an excerpt from a land use plan, but an excerpt from the cadastral map. The coloring is typical ALKIS (Official Real Estate Cadastre Information System) and represents the actual use. No building or planning law conclusions can be drawn from it.

baufenster (is this the correct term here

No. Baufenster means the buildable area of the property specified in the development plan.

Unfortunately, the building authority is currently difficult to reach by phone

Depending on the administrative structure of your municipality, there may also be a planning office. That would be your first point of contact.

formal preliminary building inquiry

Good idea!

is it possible to do it very minimalistic

Yes.

without a concrete building plan or drawing or so

After skimming through your state building code (BbgBO), unlike in NRW, you apparently need a person authorized to submit building applications in any case. The following explanations apply to NRW. To what extent this can be transferred to BB, you should clarify with the building authority.
A concrete building plan is not required, but a site plan is. Your map excerpt is already quite good. If the path located to the east is not publicly dedicated (ask the municipality in charge), the street to the north should be shown. In this case, you should find out whether the owner of an adjacent property might grant you a building servitude for access. To clarify, you should also sketch a possible building body (rectangle scaled 10m*14m) with a reference that location and dimensions are not subject of the preliminary inquiry, but only the fundamental buildability with a single-family house (or whatever you plan).

Thank you for the answer!

The street along the property belongs to the city - so the development obligation from the neighbor is unnecessary, right?

Do you have any idea who is authorized to submit the building application? At first, I thought it was me as the future builder... But maybe it refers to an architect or something like that.

After all, it is "only" about the first fact on the long way to the house.... Oh man...

These are architects and, if applicable, engineers.