Construction costs are currently skyrocketing

I can't contribute anything helpful, but I can say that we feel the same way. Fortunately (or unfortunately?) we are not as far along as you: we are still waiting for the approval of the municipal development area and therefore currently don't even have a plot of land. Nevertheless, the topic of building a house has been a central desire for 3-4 years, which we've been consistently engaged with, and which is currently dissolving into thin air.

I blame myself quite a bit because there were one or two opportunities. If only we had bought the at-the-time completely overpriced plot in 2020, or if only we had just taken the stupid developer semi-detached house with a tiny north-facing garden in 2019. In both cases, we would now have a house with a financing rate that is insanely cheap by today's standards. Instead, our equity is practically evaporating and there is no hope in sight. I can easily imagine how you and others feel who are already further along in the project.

That would of course be an option, to reorganize the whole thing again like that. That delays the entire project even further. We only have the KfW 55 standard anyway. But nothing is set in stone; if we don’t build according to it, we simply won’t get anything.

KFW55 you basically "have" to build now, as that is the new minimum requirement. However, this is no longer subsidized. At most, there is still the KFW program for home ownership. The subsidized loans per residential unit are KFW40.

And we would also be lucky to receive the subsidy for the 55 standard twice.

Oh, your financing has been completed that long already? So including signed contracts, and you're basically now in the grace period without fees or what? o_O