Construction costs are currently skyrocketing

I didn't say that.

Yes, it was clear in 2020 that energy costs would politically be forced to rise sharply in the coming years.
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That's why we factored in upwards of 100k for a renovation. With the effect that you actually didn't need to place a bid anymore, because the houses were then far too expensive. For the purchase price plus ancillary purchase costs plus partial renovation, I could build new in a similar location, including land, kitchen, outdoor facilities, and have a standard that clearly surpasses the renovated house.

It was exactly the same for me. From the beginning, I looked at how to bring an older renovation house up to the present. For that, you obviously need more than just a bit of paint and maybe a new window, and the price of the renovation basis must not be too high. Now the market has adopted this view and priced in the defects. That's where a quick €200,000 bubble surcharge is taken out of the property, and it still has to be energetically renovated.

Quite a dilemma now for someone who can manage neither the value correction nor the renovation. But also pretty much self-inflicted.

There is currently an agency report going through the media about living space per capita. Here is the graphic. It is very clear that at least a larger part of the average living space per capita is likely due to the increasing proportion of single households, especially older singles.

Which was clear to anyone with some insight into demographics and the housing market. But media and politics wanted to fuel a narrative about land consumption and space-hungry residents who simply do not want to recognize the advantages of a Berlin rental barracks from the (pre-)last turn of the century. Thus, the “evil” families with 2-3 children in the even more “evil” single-family house or semi-detached house have often been associated with 50m² per capita..

You just have to artificially (state) restrict new development areas, and you will again get great prices for these houses because they can/may be demolished and newly built there

Then calculate these cases for yourself - in urban areas you might still manage to convert a single-family semi-detached house or a row of three, but without densification it rarely becomes a good business, because prices are still quite high. Construction anyway, and purchase & demolition as well. Especially since the heirs usually are not in a huge hurry and speculate on falling interest rates..

Yes and no. In the scope that it is supposed to come according to the EU Building Directive, that was certainly not foreseeable. That you have to expect investments in an old house with poor energy efficiency, okay, but the decision-making power over the "when" and "how" was still with the owner. Meanwhile, there are legal deadlines and regulations raining down, and the homeowner is basically just an order recipient who has to dutifully implement everything.

I don't entirely agree with you. The question of how is largely foreseeable. Bringing a house from the 70s with 300 kWh/sqm into the 2020s, what does that mean? That means: new windows, insulating the facade, basement ceilings, and upper floor ceiling. For an inhabited attic, roof insulation usually means insulating on top of the roof and therefore a reroofing, because the old rafters are too thin for insulation between rafters according to today's standards, and rarely does anyone want to lose room height. All of this is clear, even without any concrete regulations. The majority of the costs are caused by the work itself. The regulations then usually only make a difference of a few centimeters in the specific insulation thickness.
The question of when is also clearly visible. Politics sign agreements to reduce from X, which then also have to be implemented in practice. With 40 million residential units and a corresponding share of unrenovated old buildings, it is completely clear that you cannot start in 15 years if you want to achieve any specific goal by 2040, 2045, or 2050.
By the way, the politicians who sign these agreements are democratically elected. Except for the AfD, all parties basically support CO2 reduction, and in all surveys, a majority of the population still speaks out in favor. Only when this approval leads to concrete consequences in everyday life are everyone against it and tell themselves the story of the evil politicians and the order recipients. To me, this is a classic case of cognitive dissonance.

People prefer to buy an expensive car or go on vacation and think they can let their house fall into disrepair for 50 years without renovation.

Well, that certainly happens. But at least with my parents, I also see that even someone who has actually kept their house in pretty good condition is currently struggling with what to do about the heating issue. Parts of the house must be around 100 years old (I’d have to ask again for the exact year of construction), but I say parts deliberately because so much has happened to the house over time that you hardly notice it anymore. Among other things, there used to be a stable that, during my grandparents’ time, was completely gutted and rebuilt inside (that part now has quite thick exterior walls, also interesting to see). Since my parents have owned the house, a lot of energy-related work has also been done: first the facade was insulated and clad with brick slips, then the rest, windows replaced, meanwhile the basement was dug out from the outside once and insulated and waterproofed, solar thermal panels on the roof. Over the last 30 years, a mid six-figure sum has flowed into the house. The house is not neglected. You could have also bought a new building for that money (which probably would have been smaller though. Currently there are 2 tenants living in the house).

And yet it is unclear how to actually tackle the heating issue now. Yes, a lot of insulation was done, but the idea that a low-temperature heating system should be the goal was not foreseeable at the time the insulation was done. Opinions differ widely on whether the current state of insulation is sufficient to operate an at least somewhat efficient heat pump with just a few measures (replacement of a few radiators, renewing insulation in the roof). And the fact that experts are sometimes hard to pin down and sometimes simply disappear after the first two conversations doesn’t help either (last year a heating load calculation was commissioned and at some point nothing more happened and the person responsible didn’t get back in touch... and overall this was not the first one who simply vanished at some point. And because there were other private matters, it hasn’t been pursued further so far – it feels like finding experts and keeping them engaged requires an enormous amount of personal effort. Overall, there seems to be so much demand that projects requiring a bit more brainpower seem to attract little interest). Currently, the status is "we hope the heating holds up a bit longer and continue saving." There also seems to be some more activity currently in the heat pump market, also moving towards medium/higher supply temperatures. So let’s see where that goes. But the point is that what used to be recommended until a few years ago for a house like this (usually gas or pellet heating supported by solar thermal) is already outdated today (or opinions are split about 50/50), and then to blame people saying "that was foreseeable" or "you just shouldn’t let the house fall into disrepair"... well...

I don’t want to deny that there are also cases where little to nothing has been invested in the house. There is a large proportion of buildings with renovation backlog. But even among those lying somewhere between "unrenovated" and "new build standard," the problem is that the target condition has (more or less) changed quite abruptly. Or partly there is still disagreement today as to what the target condition should be and what the best way to get there is...

Well, it surely exists. But at least with my parents, I also see that even someone who has actually kept their house in pretty good condition is currently struggling with what they should actually do about the heating situation. Parts of the house must be around 100 years old (I’d have to ask again for the exact year of construction), but I deliberately say parts, because so much has happened to the house over time that you can hardly tell anymore. Among other things, there used to be a stable, which was completely gutted and rebuilt on the inside during my grandparents’ time (that part now has quite thick exterior walls, also interesting to see). Since my parents have owned the house, a lot has happened energetically as well: first the facade was insulated and clad with bricks, then the rest, windows replaced, meanwhile the basement was dug out from the outside once, insulated and waterproofed, solar thermal panels on the roof. In the last 30 years, mid six-figure sums have gone into the house. The house is not neglected. You could have also gladly bought a new build for that. (which probably would have been smaller though. Currently there are 2 tenants living in the house)

And yet it is unclear how to actually tackle the heating issue now. Yes, a lot of insulation has been done, but at the time when it was done, it was not foreseeable that a low-temperature heating system should possibly be the goal. Opinions differ widely as to whether the current insulation status is enough to operate a somewhat efficient heat pump with a few measures (replacing a few radiators, renewing insulation in the roof). And the fact that experts are partly hard to reach and sometimes just disappear after the first two conversations doesn’t help either (last year a heat load calculation was commissioned and at some point nothing happened anymore and the person in charge stopped responding… and overall that wasn’t the first one who simply disappeared at some point. And since there were other personal matters, it hasn’t been pursued further so far – it feels like finding and keeping experts on track also requires an enormous amount of one’s own effort. Overall, it seems there is so much demand that there appears to be little interest in projects that might require a bit more brainwork). Currently, the status is “we hope the heating system will last a little longer and keep saving.” It also seems that something more is happening in the heat pump market right now, also towards medium/higher flow temperatures. So let’s see where this journey goes. But the point is that what was recommended until a few years ago for such a house (usually gas or pellet heating with solar thermal support) is already outdated today (or opinions are split about 50/50) and then to blame anyone with “that was foreseeable” or “you just can’t let the house fall into disrepair”… well…

I don’t want to deny that there are cases where little to nothing has been invested into the house. There is a large share of buildings with renovation backlog. But even among those that lie somewhere between “unrenovated” and “new build standard,” the problem is that the target state has changed rather abruptly recently. Or partly there is still disagreement today about what the target state should be and what the best way to get there is…

Exactly how it is. It’s not black or white. Since 2017 we have had our house from 1921 and have already invested a lot in renovation and energy-related renovation. And not everyone has 7000€ monthly income or whatever you often read here, or an inheritance or whatever. Since 2017 we have invested about 90-100,000€. Since the 60s (at least) something has always been done on the house. Nobody has lived here who didn’t invest. The alternative would have been to keep renting and pay off the landlord’s condominium. You can’t blame anyone for that. We currently have a facade from 1993 that already has insulation and is still perfectly fine. Of course, today you would insulate much more and in regard to the heat pump, we will still do that. But the money doesn’t just pile up in the basement with us and we can only do what the budget allows. Little by little. And where will it be different for those who now live in a new building, because in 30 years or less it will already need renovation and then I want to see how much those people care about what they have to do and how they pull one or two years’ salaries out of their sleeves without batting an eye. Then I wish everyone here that no one ever becomes unemployed or sick or otherwise struck by fate and that you have always built up reserves.