Real estate purchase preliminary contract - demolition and new construction - costs?

Hello everyone, who can explain this to me? I want to buy a house but without a real estate agent. Now I have received a preliminary contract and do not understand this paragraph. Do I have to pay the difference for the land if I demolish the house and want to build a new one? The land is not leased.

what does the broker or notary say! they get money for it

Beforehand: Consult experts aka notary. Only they can explain this to you with absolute certainty.

Lay interpretation: The seller (the city of Hamburg?) wants to protect themselves against speculators and participate in potential value increases after further construction measures? The plot is sold at value X/m², and there is apparently still room for more houses. The area could "develop" and the standard land value could increase (X+n/m²).
If the new owner now builds apartments, they also benefit from the higher standard land value / the greater attractiveness of the area (through the sales price). The city now wants to skim off a part of this "unearned" profit (since the increase in value is not caused by the owner but, for example, by public infrastructure measures).

This looks a bit like a "urban development measure" on a small scale (-> google).

That looks a bit like a "urban development measure" on a small scale (-> google)

Yep. It is absolutely common in larger projects that the purchase price of the property is adjusted depending on the utilization of the property. This also increases the value of the property.