Floor plan of a single-family house with basement, 150 sqm, only single-story allowed

The bay window may undercut the 2.5m clearance area (for me it is currently 3.5m without the bay window) to 2m.

It does not matter whether you call it a bay window or what conditions a bay window is subject to. A living room will not be approved at the property boundary.

That was the explanation why this wall is being planned. The wall separates the bay window (and thus the house) from the bicycle garage. Therefore, this bay window part counts towards the ground floor area. This allows the knee wall to be higher than if the bay window is omitted and the whole "annex" is designated as a bicycle garage.

You are doing it again and associating your bicycle garage with a knee wall. I think you are mixing far too many things together to want to calculate anything.

The bay window (which is included in the floor area) also does not reach the property boundary but maintains a 2m distance:

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Has anyone already dismissed this structure together with the bike garage like an architect? I doubt that this construction fits within the setback areas. And I still do not understand:

Die Wand zwischen Speisekammer und Fahrradgarage wird später nicht gebaut.

Has anyone already stamped this structure together with the bicycle garage like an architect?

Yes. My parents have also done exactly the same in the same village. The room will later not be heated (or only up to the frost line). So it is really no living space. Leave out the bay window. The bicycle garage follows immediately after the kitchen, where beverage crates are also stored. No bay window and no partition wall.

So a bicycle shed pantry divided by a virtual partition wall with the thickness of an exterior wall is supposed to be a pantry up to the merely drawn partition wall, be called a bay window, count as living space for the ground floor, and thus inflate it as the calculation basis for the non-full-floor attic, so that the attic with a higher knee wall does not mathematically fail to meet the standard for a full floor. At the same time, the virtual partition wall is supposed to ensure that the bicycle shed pantry up to this line can be declared a bicycle shed in order to fraudulently obtain a boundary privilege. At the same time, a slightly shortened boundary distance of the denominator bay window is to be fraudulently obtained. A rather complex, multiple, and preposterous building code violation for a somewhat higher knee wall as a straightforward approach. Who exactly is one trying to successfully make a fool of with this?

So a bicycle shed pantry room divided by a virtual partition wall the thickness of an exterior wall is supposed to be a pantry up to the only drawn partition wall, be called a bay window, count as living space of the ground floor and use this as the calculation basis for the non-full-story attic, so that the attic with a higher knee wall mathematically does not exceed the limit as a full story

That is correct.
The rest less so, because the border privilege is neither faked nor swindled.