Construction costs are currently skyrocketing

Do you already know the tariff from Qatar, when all Western countries get their gas from there?
Honestly, I don’t think we will ever see gas prices below 15 cents/kWh again...

Which could lead to electricity prices around 40 cents, as seen in some current new customer offers. And photovoltaic self-consumption in winter reduces only a part of old building heating costs even with a large, unshaded south-facing roof. But of course, with photovoltaic at prices like two years ago, you could possibly make the heat pump somewhat more attractive financially. However, that also means many thousands of euros higher investment again.

... With electric cars, the belt is supposed to be tightened soon as well. Somehow, the whole scrapping of various subsidies conveys an austerity course of the government, if it weren't for the distribution of tax money around the world – oops, I didn't want to start a political discussion, just express my subjective, perhaps slightly irritated opinion on the overall situation. ...

Here (and with heat pumps, photovoltaics, ...) the question is also what happens when you shift the demand curves through subsidies with a "capped" supply (supply chains) – which was partly seen with the fuel discount. It's clear that such erratic action is not ideal for long-term investment planning, but the cutting of subsidy programs is certainly not just about austerity, but also about fighting inflation.

Renovation of existing buildings is apparently not desired? I can understand that one has to budget and that subsidies are not always viewed positively from the end consumer’s perspective. But that’s really a tough nut to crack...

There is no need to subsidize with tax money what is already profitable anyway.
Everything done correctly. This also applies to the reduction of the e-car subsidy.

But the truth also is that people who built a single-family house 20 or 30 years ago are now living in a place that requires 150, 200, 250 kWh/m²/a for heating annually. That quickly adds up to 20, 25, or even 30,000 kWh/a... 20,000 kWh cost around 4-5,000 EUR at the end of the 2022/23 heating period.

Yep, exactly. This calculation then affects people like my aunt. He works at the local public works department, she is a childminder. They have three children who are just becoming adults but are not yet financially independent. I would be surprised if they simply had 5,000€ left over. Just so we don’t misunderstand each other... as an ordoliberal, I am not exactly a fan of subsidies and funding. Currently, one massively benefits from renovation due to high energy costs, and the effect of subsidies on prices is also problematic. But there are also many people who can hardly afford the renovation, and for these people there must be a solution. That's why I find a subsidized loan with some repayment allowance not wrong.

Currently, one massively benefits from a renovation due to the high energy costs, and the effect of subsidies on prices is also problematic.

With all understanding for the hardships that sometimes occur: Either a renovation is worthwhile or not (also taking into account the future development of energy/emission prices). If it is worthwhile, then it can and should (financed externally, e.g., with KfW, but without repayment grant) also work without subsidies. If that is too expensive, or a renovation is not worthwhile (but not renovating is also _long-term_ too expensive), then the underlying problem is: For the respective owners, the single-family house (unsubsidized) is too expensive a form of housing. Now, of course, one can subsidize to make living in this form of housing affordable, however: Is that money well spent (from a societal perspective)? Are there not more efficient forms of housing that could be promoted? Apart from that: I wonder, especially with the mentioned 20–30 years old houses, whether there might have been a lack of maintenance reserves from the very beginning. Perhaps the single-family house was actually not feasible from the start (calculated honestly), and the collapse comes exactly when the first major renovation is due.

Isn't there more efficient forms of living that could be promoted?

Does it say anywhere that the subsidy only applies to detached houses? Did I overlook that? With apartments, the situation is even worse. The tenant pays the additional costs, the landlord the renovation. The modernization surcharge is a bad joke as an incentive. Will anyone renovate without subsidy? Certainly not.

Aside from that: I wonder, especially with the mentioned 20–30 year old houses, if there wasn't a maintenance reserve missing from the start. Maybe the single-family house was (honestly calculated) actually not affordable from the outset, and the crash just happens when the first major renovation is due.

Surely it was calculated very tightly. But politically, homeownership (whether house or apartment) has been promoted for a long time, keyword homeownership allowance. And in rural areas, you hardly have any alternatives to your own house. Renting an apartment with 3 kids? Good luck with that search.