4 years after construction, the office also demands land acquisition tax on the house

Again. For the private homeowner and their rather small real estate transactions, the advice of a notary is usually free of charge, as are, for example, explanations or consultations regarding [Nießbrauch] or [Erbrecht]. Specifically regarding [Erbrechtsberatung].

Those who do not want it for free can always get paid advice from a lawyer.

It is not unusual for a notary to issue a bill for highly complex advice in the real estate business of investors.
However, this does not affect any of those present here.

Not quite, the notaries in state service (state officials) were abolished at the end of 2017. Freelance notaries with their own district are still the only notaries in Baden-Württemberg, Bavaria, Brandenburg, Hamburg, Meck-Pom, Rheinland-Pfalz, Saarland, Saxony, Saxony-Anhalt or Thuringia.
(Yes, I have one in the family and am quite sure about that ;-) )

Also in certain parts of NRW.

Can something like this also happen due to the temporal connection of two otherwise independent contracts? Even if it involves a municipal property with free choice of developer? I once read something of that kind somewhere.

Can something like this also happen due to the temporal connection of two otherwise independent contracts?

No. That can only happen if the contracts are linked. So no free choice of the construction company.

No. That can only happen if the contracts are linked. So no free choice of the construction company.

No. That can only happen if the contracts are linked. So no free choice of the construction company.

Thank you. I found the following on the internet:
"Important: Both contracts must be separated in time and content. There should be at least half a year between them. And you should not buy the land from the company that builds your house."

Can something like this also happen due to the temporal connection of two otherwise independent contracts? Even if it involves a municipal plot with free choice of developer? I once read something along those lines somewhere.

Yes and no. Of course, it can happen, but it must not. And it is also not lawful. However, it does happen, especially when the two contracts are concluded in close temporal proximity. Some therefore take the safe detour of concluding the plot in the old year, the contract in the new year. And it is also important not to speak of the developer, but of the general contractor (GU), because a developer sells house and land together.