Number of stories - second full story only if it forms the attic

I just don’t think that the knee wall can be made arbitrarily large.

Asked the other way around: if not, how is the upper floor supposed to become a full floor?

For that, it would have to break the full-floor bar. However, that probably requires a substantial knee wall.

Yes, because the answer to the OP’s question

you owe us.

Forcedly, since I am not the building department official. I have indeed speculated, similarly to you,

The building type "urban villa" is excluded by the development plan, since the 2nd floor is not an attic floor. Does it perhaps already become an attic floor if I simply leave out the ceiling to the roof structure or maybe start the roof structure at 2.45m?

that such open roof undersides could create a combined full-and-attic floor. However, because of the minimum 28° roof pitch, I discarded that again, as that is, first, an "upper limit" for me, and second, the roof pitch suggests wanting to enable standing height in the attic.

Therefore, I switched to considering it more likely that only "zero living space" in the sense of the land use ordinance may exist above. But

I find the question very exciting and certainly worth discussing.

and best of all if the OP would obtain a statement from the responsible authority. Because if we contribute different assessments, that probably creates more confusion than clarification. For that, a "responsible person" is needed—"experts" (also with different backgrounds and opinions) are not enough.

What quarrel do you mean? I find it interesting how some city planners make life difficult for builders, architects, and approval authorities with impractical regulations.

By quarrel I mean when conflicting views are asserted with the same certainty. And the questioner mainly gains uncertainty :-(

One of the discussants is a surveying engineer, who is at least adjacent to the field. Another is a management consultant, who at least stereotypically always has knowledge inversely proportional to their opinion—but of course you can never be totally sure. And then others join in, and the questioner wants to shout: "Broom, broom, you are gone!"

Only the one who devised this full roof floor (or full attic floor) can "decisively" clarify. He must know what ideas drove him there.

Why didn’t they simply set minimal and maximal eave and ridge heights?

That would be, if you also added the floor area or building mass number, the ideally proportional development plan from my side. You don’t need this nonsense of also creating catalogs of front yard shrubs (of course within the botanical horizon of the municipal council) for peace in the building area.

if not, how is the attic supposed to become a full story then?

Quite simple, with dormers. A full story is defined by the area (e.g., 2/3 of the area on the ground floor).

That, however, probably requires a substantial knee wall.

I don’t doubt that at all. But I would interpret 2.45m knee wall with 2.50m clear height as circumventing the zoning plan regulations.

Because if we contribute different assessments, that will probably cause more confusion than clarification.

I don’t see it that way, because if people who think they know say

I would have this view confirmed by the local city planners, since I do not know of any definitions of attic floors in laws and regulations.

and no one replies who actually knows, that can certainly be helpful in preparing for talks with the decision-makers.

And the questioner mainly gains uncertainty then :-(

Or the certainty that their question is very legitimate.

This nonsense

And there we agree! According to the zoning plan, the OP could put a 27m*10m house with a 45° gable roof on their plot, where due to the sloping terrain the basement would not count as a full story but would be habitable,
and the attic space with a 13.5m gable triangle and Xm knee wall would allow room for four stories. Result: ridge height above the street approx. 20m. Is that urban planning-wise desired?