Assessment of financing scope with 4620 euros net

How they do it, you better ask them yourself...

The bank calculates a flat rate of €500/month for a car, living expenses for 2+1 at least €1500, €1500 installment and €500 additional costs, so everything is gone per month with full salary, parental leave is only 65%, so at least another €700 per month is missing there.
In addition, you basically cannot show any equity capital. With a suitable story, e.g. early 30s, both studied a long time, loans paid off, it still makes a reasonable picture. A few years later it gets more difficult. Your initial calculation includes >€3k savings rate, effectively it is only a fraction, why should the banker believe you for the rest of the story? The overall picture simply does not seem consistent.

€400k house plus additional costs ~€60k (15%) at 2% interest and 2% (absolute minimum) repayment thanks to 115% financing over 10 years would be a €1533 installment. The poor loan-to-value ratio or lack of equity capital spoils your plan or drives the interest rate massively up.
By comparison, with only 80% loan-to-value a few months ago, with otherwise the same parameters, an interest rate of 0.9% would have been realistic and with the same installment a loan amount of €630k would have been possible.

So it has to be affordable on an average pension.

What does the latest pension notice say? Doesn't it also include an estimate with inflation adjustment?

I just don't understand how acquaintances can set up 650k houses with 0 equity, 1200€ installment

That's just a lie. Do the rough calculation: 650k / 1200€ / 12 months equals 45 years until the house is paid off. Without interest calculated!! That doesn't add up. Presumably, far more than 100k to 200k in equity went in to get such an installment.

I also live in the area. Prices - disaster. I can't understand why the land here is so expensive. Sure... A6, A81, not far from S. But... no ICE, airport almost 70 km away... In HN, you can get plots from private individuals starting at €800/m2. From the municipality, like the OP, about €400-500. Simply insane...

We managed to get a municipal building plot in a village (18 km from HN). Strict allocation criteria based on social points. No bus, the nearest S-Bahn is 5 km away for..... woohoo €320/m2. A real bargain... :mad:

The region is just doing too well :) The Schwarz empire pays very well, Audi is here and then there are some suppliers whose names we don’t even know. Besides, HN itself serves as a catchment area for Bosch, Daimler, Porsche and co. Further towards Nuremberg on the A6 are Würth and Ziehl-Abegg, Stahl, Gemü and whatever they are all called. Walldorf is also not that far away. So everyone who works in the direction of Heidelberg or Stuttgart but finds the prices there too high can look towards HN.

They then take the building plots with the highest bid...

you keep hearing the argument of demographics.
But what this line of reasoning overlooks are social and medical developments. Firstly, fewer and fewer people live on more square meters. Secondly, people are living longer.
Nevertheless, there will of course be vacancies, but primarily in regions already affected by rural exodus.
That has zero impact on average rents in metropolitan areas.

What does medical development have to do with demographics? It is and remains a fact that the largest cohorts are at the top, while in the critical corridors for house building and buying there are fewer and fewer demanders. And with each year of the bubble, larger cohorts are pushed out of the grid than are pushed in from below. This is exactly the kind of case we are discussing here.

You also, like many, did not understand the square meter statistic. Because it must also be seen and read in relation to age. That's right – there are plenty of elderly who sit alone or in pairs in huge houses and apartments. These (especially from the 1980s, 1970s) are often larger than the shoeboxes still being built today (real, not here in the forum). The family with many children (today 2 or more) sits in the 3-room rental apartment with 70 m² and hopes for another room. But since the demographic cohorts are so small, they do not compensate for the widow on 200 m².

Just so I understand correctly, an existing property for around 400k wouldn’t be feasible either, right? Even with, say, realistically saved equity of 50k? And also not a standard semi-detached house with 260m2?

My example with the 400k was chosen arbitrarily :) But if you look at the existing stock, you will see that you would still have to invest a lot there. Which brings me back to the amount of own work. I have rarely seen bargain houses. And those that I did, still had a lot to be done.

After last year's price rally, in my opinion, 650k for a new build is also quite difficult considering the land price, unfortunately. Condominiums of a good size are also quite expensive here, unfortunately.

What you can do is visit your main bank to see what kind of loan they would offer you. Then you might have a better idea of what is actually feasible.