Semi-detached house in building area 8.5m x 15m (WxD)

I have adjusted this a bit to reality. I would position the first entrance 20 cm higher than the street and the second one 60 cm.

That is an interesting approach that I hadn’t considered yet. Thanks! What speaks against raising the rear (here: right) half enough to allow level access to the garden? Or in other words: How and from which floor does one enter the garden from the rear gable side?

... could you add a few measurements to your floor plan drawing? And, weren't 2 offices required?

Many things are possible.

In the boldest case, perhaps also an asymmetrical gable roof with the ridge over the rear half (and in a way a shed roof over the front), to be able to set the rear one story higher...

maybe it gets annoying in the long run to thank every time. But I am genuinely impressed! In some other forums, there is the possibility to "buy a coffee" for other members. Too bad this is not possible here. How can one show appreciation?

Here there are officially not even other forums yet. For me, thanking happens via Paypal.

I did not ask for a purely street-parallel division,

That would also be absolutely illusory; for the house format, "bowling alley" would not even be an expression.

but for a pipe-stem/hammer-shaped plot with its own 3m wide access road. At that moment, the previously positive mood in the conversation suddenly flipped. Apparently, I had poked a hornet's nest.

Not a hornet's nest, but all I would have done was drop the expression from my face. Because at least up to the middle of the pipe stem, a lateral building setback would have to be observed again; such a division would already be a mutilation of the property.

This is an interesting approach that I hadn’t considered before. Thanks! What speaks against raising the rear (here: right) half enough to allow level access to the garden? Or put differently: How and from which floor do you get to the garden on the rear gable side?

I had actually sketched that first. But I’m not sure if the base height argues against it. In any case, that’s an approach. Breakfast terrace at the setback level of the ground floor. Secure with L stones towards the neighbor. If there is a height plan, more detailed planning is possible. Pictures of the property are also quite helpful.

... could you add some measurements to your floor plan? And, weren't 2 offices required?

Too much work. Outside 7.5*8.5m. The 2nd office can also be accommodated in the attic.