Which building regulations make new constructions so expensive?

Well, if something does happen, he will have to pay for it his whole life. Germany just pampers its residents and the US are largely still stuck on the idea that the state should only provide security and infrastructure and otherwise keep out of it. It then tends more towards self-organization with Home Owners Associations and so on. So in the suburbs, the municipality might not make (many) regulations for you but instead the neighbors do, and then really strange things, like not cutting the hedge on Sundays without [Oberköroerfrei].

Why don’t you start on the other side?
Imagine someone planned a 5-story building right next to your fancy single-family home in a cozy area because it’s a good location.
You’d be up in arms about it too.

You can take a look at the specific example with Hafner. Apart from the usual blocking groups, I don’t know of any group that is seriously against the development itself. There aren’t many who could be bothered by it. Maybe a few allotment gardeners. The problem in this case is more that people from elsewhere don’t find good enough to be good enough; everything has to be especially great.
Of course, there are other cases, e.g. Jungerhalde West, where the residents simply don’t want socially subsidized neighbors and then declare the potato field an ecologically valuable biotope ;)

Nowadays, you can still build affordable houses, but if you want to tap into Kfw funding or have the best self-sufficient heating, it gets expensive.

I don’t agree. Already two years ago, with Town & Country, without a basement and hardly any upgrades, but including a 70k plot, additional building costs, kitchen, outdoor facilities, we barely stayed under the half-million total budget. That’s not cheap for average earners. With 20% equity, that was already a loan of 400k or a 1500-1600€ payment if you want to be finished relatively quickly. Today, it’s even worse.
But I’d gladly accept a counterexample from you where you can still get an affordable house today.

In China, the next day there would be a sign on your door saying something like "We are building a residential complex here for 25,000 workers, in 4 weeks the excavators will start, pack your stuff. As compensation, you will get an apartment in the new residential complex."

That is not true, expropriations are very difficult in China. Try searching for "china refuse to sell"

Already a loan of 400k or a 1500-1600€ installment, if you want to be finished somewhat quickly.

Maybe this is the crux of the matter.
The goal of having to be debt-free by retirement could also be given up. It is enough that the installment is reasonably low from retirement onwards, then the loan could be continued indefinitely.

I wouldn't. In 30 years, the new buildings of today simply won't be new anymore. Then windows, heating, etc. need to be replaced, and that costs money. In retirement, you generally have significantly less money available than during your working life. There are cases where you can extend financing into retirement, but strictly speaking, they are not dependent on the financing. Anyone who financed a term of over 25 years during the low interest rate period has clearly overstretched themselves.

I wouldn’t. In 30 years, the new buildings of today simply won’t be new buildings anymore.

Yes, it’s no longer a new building, but still far from needing renovation.

Then there come , , etc. and that costs money.

Come on, windows have a lifespan of at least 50 years. Most homeowners will not live to see the end of their windows’ life. A new heating system doesn’t cost the world either. €4000 for a new condensing boiler. Those who own a more expensive heat pump can save accordingly. Which brings us back to the topic: heat pumps are cost drivers. One should definitely have reserves for a new heating system.

In retirement, you usually have significantly less money available than during working life.

Correct, therefore you can accordingly reduce the payment when entering retirement (halve it?). Simply stretch the remaining debt over 30 years again. It will still be cheaper than renting.

Whoever financed a term over 25 years during the low interest phase clearly overextended themselves.

No, because prices exploded with the low interest rates. That balances out.