KFW40(plus) as a prefabricated or solid house with "modern architecture"

I also think you are in good hands with an owner-managed carpentry company, even if it is larger, perhaps even better than with a nationwide prefab house builder. You make the preliminary contract with the boss after mutual getting to know each other, still with a handshake, and you are not just number 14376. That’s how it is with us. We have never regretted it, no major problems. If something did come up, it was solved fairly for both sides in a joint conversation. No surprises when checking or changing on the construction site. All subcontracted trades have known each other for years and have also helped each other when necessary. The offered "standard" was also better at an even better price than with the big prefab house builder. He simply does not have to pay for salespeople, show houses, or advertising. His advertising is his satisfied customers.

Are we also talking about prefabricated houses here

Timber frame construction - which is presumably equated with prefabricated houses again here - is by no means cheaper nowadays. That's how your statement comes across?! Pay attention to the wall construction of various companies, from that you can see who builds with high quality and who does not.

Good luck!