Application for plot of land for semi-detached house

I once had that with a construction project I was interested in. All projects had to be financed by the Umweltbank, which required 30% equity. But that was back in 2013 or so.

Bank commitment can certainly exist just like developer commitment – but even then you don’t submit a joint financing application. Semi-detached house partners are not partners with each other, do not form a partnership or anything similar. If I build or buy a semi-detached house, my neighbor and I know nothing about each other’s data and are not lumped together in the same credit check. So the OP can safely assume that for the bank, he does not have to mentally count his half twice.

Only additions to the other notes:

As I understand it, for a financing confirmation from a bank, among other things, information on the specific plot of land as well as the building project including prices must be provided.

The bank does that all the time. They already know what to do.
However, you should roughly estimate your costs, see the construction cost subforum here.

Since the building project here is a semi-detached house, I wonder how one can provide information on this without having spoken to the future neighbor of the second semi-detached house since the allocation has not even taken place yet?

That is irrelevant for now

The expectations can be totally different. You somehow have to "fit together" directly, right? What are your experiences?

Semi-detached houses do not always have to fit together. In theory, a Bauhaus style next to a hip roof would also be possible – the shared boundary construction counts. You can also just put the garages in the middle, linking them.

According to the development plan. Thus, this should be given to the semi-detached house providers at the beginning, correct?

The development plan is the bible of BU (builders).
So first just relax after you have done a proper calculation.