Is building a house financially feasible?

Ownership of the house is proven by the land register. But the land register only contains plots of land and no houses! After the leasehold term ends, the house belongs to the lessor (there is indeed compensation, but it only has to amount to 2/3 of the market value of the house, which for an older house can easily be close to zero)! Or do notaries also just write nonsense?

While the leasehold right (usually 99 years) is in effect, ownership of the house is not with the landowner. Only afterwards do the house and land combine into a single unit. If this were not the case, the house builder could not apply for a loan, as he could not offer the bank any collateral. Just read the information sheet in your link properly:

According to the regulation of the law, a leasehold right (simply put) is the right to have a building on (someone else’s) land. Ownership of the land and ownership of the building (e.g. residential building and garage) are therefore separate. This also applies when the leasehold right is established with regard to an already constructed building. This departs from the principle of German law that everything built on the land always belongs to the landowner — the so-called essential components.

In essence, the leasehold holder (leaseholder) — aside from certain restrictions — can deal with his “fictional” plot of land with building for the entire duration of the leasehold right just like a landowner. In particular, the leasehold right can be encumbered, it can be sold and inherited.

The ownership of the house is proven by the land register. But the land register only contains plots of land and no houses! After the term of the leasehold ends, the house belongs to the lessor (there is compensation, but it only has to amount to 2/3 of the market value of the house, which for an older house often approaches zero)!

I will save myself the cursory reading of the information sheet, because: I am registered as the owner in the land register! For this leasehold property. (Just checked, as I am currently filing and sorting and had the folder in my hands)

Or do notaries also only write nonsense?

Sometimes cursory reading as a layperson does not necessarily lead to the truth. And yes: basically, one knows that "paper" on the internet can be very patient.

I’m going to skip skimming through the information sheet because: I am registered as the owner in the land register! For this leasehold property. (Just checked since I’m currently filing and sorting and had the folder in my hands) Sometimes skimming as a layperson doesn’t necessarily lead to the truth. And yes: basically you know that the "paper" on the internet can be very patient

Almost right You are not registered as the owner of the property; the leasehold grantor is still listed there. There is a second land register, the leasehold land register. This records that you are the owner of the leasehold—you can (more or less) use, develop, etc. the property as you wish. Smarty mode off... By the way, I don’t think leasehold rights are bad; however, currently they are more expensive than buying the property because usually the leasehold grantor wants about a 5% return on the property value as ground rent. There are exceptions here as well from time to time.

Almost right
You are not registered as the owner of the property; the ground lease issuer is still listed there.

You... honestly... I unfortunately did not have much time to address everything here, nor the inclination to post every line of the land register entry here (because there are, of course, other things concerning the ground lease).
Only what Elina posted here is definitely wrong and cannot be left as is.

In essence, it counts that a property under a ground lease should not be a disadvantage for most prospective builders. You just have to deal with it.

And who would want to buy something like that if you ever want to sell it?

The lower purchase price even increases the number of potential buyers. In our search for young used properties, some houses with leasehold were within the desired budget. These houses would not have appeared on our search list at all if they included the land. I find a sale towards the end of the leasehold contract problematic.

Moreover, I could imagine that the interest rates on the leasehold contract might be somewhat more favorable since the ratio of equity to loan amount is better.

However, I do not think that a 5% leasehold interest can currently be enforced (even over 100 years). Over the term, this would correspond to five times the value of the property. Even monetized, the property would be clearly too expensive at today’s interest rate.