ETW found, notary probably only in 2021. Broker fee?

That is basically correct. But if, as I mentioned before, usable space is obviously declared as living space or roof slopes are simply "forgotten," the real estate agent is involved in that as well. He must have that much expertise.

However, the purchase contract ultimately only states the land register sheet that you are buying. In our attic apartment, the roof slopes were also "forgotten." However, in my opinion, this was not done with bad intent, as only the floor area is indicated in all documents. In other words, I wouldn't even know the living area according to WoFIV. So when we sell our apartment soon, I will only state the living area according to DIN 277 in the Immoscout listing. So in my opinion, you were lucky that the real estate agent agreed to it, as it is not his task to verify that. At least that's my opinion.