Building in the outdoor area - Repurposing the old barn into a single-family house

Yes, that would be no problem at all indoors.

The OP is talking about outdoor areas here. Read post #6 again.

Let's read the quoted law.
Projects that serve an agricultural or forestry operation.
A residential house does not serve this purpose. The law rather means a hunting lodge, a barn, or a machine hall.
[...] And especially in Bavaria, they are very strict about this.

That is the difference between a conspiracy theorist and a qualified answer.
That the building serves the operation can be argued with an architect not super easily, but still without extreme effort.

The intersection between nonsense and a qualified answer does not necessarily have to be zero.

I would also consider a forester's house to be covered by the legal purpose. At forester Martin Rombach in Küblach (which does not exist - but if it did, it would undoubtedly be in Bavaria) the manager's apartment also clearly outweighed the study.

In our area (Eastern Bavaria), the new house for the children next to the parents' old homestead is almost standard. According to an employee of our municipality, the residential unit for the manager is often linked to it.

I would also apply that here, or declare the new building as an "Austragshäusl."

There was a recent amendment to the Building Code making it easier for children to build on their parents' property.

Can you emphasize that (without a link, as you know) with a more detailed note?

In our area (Eastern Bavaria), the new house for the children next to the parents' old homestead is almost standard.

Oh yes, I hadn't mentioned it yet. This is the usual "Altenteil" arrangement. Quote from the announcement of the Bavarian State Ministry from 2021 – so that you also have a suitable basis (even though it is regulated like this everywhere in Germany). In this respect, I would like to reaffirm my personal assessment that you should have no problems with renovation or new construction given the framework conditions. Assuming a suitable architect.

It is not about a farm and a full-time agricultural operation.

Here people are hiding behind some wannabe scenarios. This is merely about rezoning an existing plot of land in an outer area for private use by building a single-family house. And exactly that will not happen.

There is already public interest in not allowing exceptions. That is just how it is in Germany.
The legislation is unfriendly to families. The building authorities come along right away with fragmentation of the landscape, landscape protection, and many other issues. I also have a 3000 sqm plot of land in the outer area. But it is only my plot in the outer area.

Below is an inner area with residential development, above is residential development inner area. Behind is the forest.
No chance for building land even though there is only 1 building plot in the 3000-inhabitant community. At least 5 houses could be built on my land, the access would go completely over my property.

The community does not want it.

I do not understand why the topic starter is still given hopes for a building permit here.

It is not about a country and a full-time forestry business.

We operate ... a forestry

Reading helps. And full-time operation is not necessary. Look for an architect and very likely build.