How quickly should one pay off a house?

And there will still be cars with combustion engines in 30 years. The combustion engine ban from 2035 is already shaking significantly.

I always find such ways of thinking funny. You really think this way of thinking only exists in Germany (often even limited to "the Greens"), right? No, it's like that worldwide.
Who is supposed to build combustion engine cars for the average German then?!
The German manufacturers who are massively dependent on worldwide sales?
Spoiler: no! And the rejection comes from the manufacturers themselves! They know from which direction the wind blows worldwide. They are not going back to the combustion engine.

Then I often read that some people stretch the financing until retirement or even into retirement. That really wouldn't be anything for me.

And why exactly? After all, you continue paying rent beyond retirement age. The loan burden, in contrast to the repayment, also inflates away by itself year after year. And if you inherit (or separate), the entire calculation will be completely redone anyway. Therefore, there is no general answer to your question. Just pay what allows you to sleep peacefully at night, remain disciplined in your spending habits, but still don't forget to live. It will work out.

Then the house will just be sold, and with the proceeds, one can enjoy life in a rental apartment without obligations until the end of their life.

Most people will find it very hard to take this step. Practice shows this. And why should it be any different here in 30 years?

In 20 years, no one will be able to retire at 63 anymore.

All the more reason to save more. Practice also shows here that by 63 (actually partly even earlier) the vast majority have really lost interest in their job.

And cars with combustion engines will still exist in 30 years. The ban on combustion engines from 2035 is already wobbling heavily.

At least not in big cities, where there are (also specifically here with us) political majorities for combustion engine bans on existing vehicles by 2040 at the latest. It’s no use to me if I’m allowed to drive my combustion engine car out in the sticks; 99% of the destinations are in the city anyway.

And when will "life" start for you then? At 65?

We actually afford everything we want to afford. Sure, you can also spend 8,000 euros for 10 days of vacation instead of 4,000 euros for 10 days, but I hardly believe the vacation would be better then, and I rather think that the so-called "buyer’s remorse" will be more pronounced (when you spend 8,000 euros at once) and you actually get less out of it net. Only when it comes to the car do we actually drive two very old cars, although our main car is rather large and has many extras (automatic transmission, a lot of horsepower, size: mid-range, so bigger than a Golf & co.), just old, but comfortable. Here one could really blow a lot more money, but on the other hand, it’s only a means to an end to get from A to B (and in the city the car itself is already a luxury; public transport or the bicycle actually also does the job). With another, newer car, we wouldn’t get from A to B any faster and basically not any more comfortably either (rather, operating comfort & quality of seats gets worse every generation).

On the other hand, you naturally wonder that you’re in such a comparatively comfortable situation (many friends can’t even afford to buy an apartment here despite double-income academic salaries). Are we maybe too frugal after all? But what would you even spend more money on?

Another example: store brands. I consistently buy store brands where I can’t notice a difference. And where I notice a difference, I consistently buy the brand products. That’s of course not necessary, but why spend 200 euros more a month for 100% brand products if I absolutely can’t notice a difference!?

The nice thing is that everyone has different "needs" and there is something different for everyone that makes them happy. We were lucky to have built at a time when interest rates were very low, and unfortunately, you can only dream of our construction costs today (245k for 140sqm, all included). Accordingly, we have a monthly rate of 631€, and in many places, you can no longer even rent a 50sqm apartment for that. Theoretically, we could already be done with the financing... we would have just had to restrict ourselves. But we preferred to go on vacation with the children... bought expensive furniture... have 3 cars... I spend 300€ - 400€ a month on LEGO because it makes me happy. For example, a car does not seem so important to you. Of course, you can get from A to B with any car, but for example, I just treated myself to my dream car for 50,000€. And it makes me happy. That is much more valuable to me than paying off the house quickly to then immediately focus on retirement savings. Not worrying too much and simply being happy is also an important retirement provision. That does not mean you cannot be happy with your idea of life, but it would not be mine. And therefore my answer to the question: "How quickly should you pay off a house?"... As quickly as you want and while you are still happy.

Idle topic. There is no real advice. What is important is that your wife fully supports whatever plan (saving, consuming, or a middle way) with conviction and not just goes along for your sake.

That will be very difficult for most people to take this step. That’s what experience shows. And why should it be different for us in 30 years?

I happened to have a conversation with my boss about this topic today. She is a lawyer, her husband is a doctor, and she said that she and many people in her circle hardly repay their loans. They don’t even want to acquire ownership. They live in a house, pay interest as if they were paying rent, and ideally want to sell the house later without loss. With the money, they repay the remaining debt and save the unpaid repayment for retirement in ETFs. That’s the short version of our conversation.

Honestly, I have never heard anything like that.

We ourselves are also dual earners and now have a higher net income than when we built. We also drive 2 cars, spend money whenever and for whatever we want, but even with only 0.82% interest, we repay 6%. We still have a remaining term until 2032 and are now saving the special repayments we planned annually as a monthly savings plan in an ETF. But the money is also out of our heads; whatever comes, we don’t touch it. We want to be done by 2032. Logical as everything else sounds, it is simply firmly ingrained in our minds that we want to be free of the construction financing.