Construction costs are currently skyrocketing

Your calculation only works if the place is debt-free. And that is probably not the case for most readers here, most real estate millionaires still owe a lot to the banks.

I assumed that since the question was: what should I do with the million.

No matter what my house is worth, no one will get me out of my Bavarian village anymore.

That's why 25-year-old prospective buyers come to me who plan their lives in an "age-appropriate" bungalow. Built once and planned to stay in the same house and the same town for the next 50 years... how bleak. How much freer and more interesting do, for example, Americans, English, Swedes, Dutch, etc. live. They buy and sell houses/apartments as it fits their life planning. I have lived in Hamburg, Berlin, Freiburg, Saarbrücken and now here. I would die if I knew I had to stay in one place forever. How many interesting experiences and phases of life would I probably miss.

I have been living in Berlin for 20 years and thought I never wanted to leave here (before that, by the way, also Hamburg among others) Now that I am building here, I can very well imagine it. Now the place just has to be finished and worth over a million...

How much freer and more interesting do Americans, English, Swedes, Dutch, etc. live. They buy and sell houses/apartments as it fits their life plans.

But one must also consider the costs incurred in the respective countries. Nowhere is it as expensive to buy and sell a house as in Germany. Especially if the loan has not yet been fully serviced within the agreed term. Then there are the loan conditions, which are particularly strict here... the requirements for renovations, remodeling,...
My cousins in Sweden usually bought their first apartment while studying, later sold the apartment, then bought the first house with their partner, and later a bigger house when they had children. My parents handled it similarly in the USA. I, fool, thought I had to stay in Germany and only just bought my first house in my early 40s. I’m already looking forward to Thanksgiving when I can tell the family stories from the administrative jungle. :D

I have been living in Berlin for 20 years and thought I never wanted to leave here (before that, among others, Hamburg)
Now that I am building here, I can very well imagine it.
Now the place just has to be finished and worth over a million...

Goslar -> Hannover -> Berlin -> Beelitz -> Construction in Fichtenwalde.

Why move 1000 times? I prefer to travel and take a good look at the cities.

I don't have to move 1000 times. But I also don't have to force myself to put down roots. I could well imagine moving to the Harz. Isn't it nice there?