Whether someone from the building authority actually goes through the streets to check who has carried out unauthorized construction measures is rather unlikely.
I see it the same way, especially since in Brandenburg, as in most (or all?) federal states, uncovered terraces are exempt from approval. The neighbor has to provide more than just a tip before the building supervision intervenes. That you do not need a permit of course does not mean that you do not have to observe the regulations, such as the stipulations of the development plan. If you build contrary to the stipulations outside the building window or exceed the floor area ratio, that would be fodder for the unpleasant neighbor. However, the neighbor would have to be very well versed in building law to formulate a complaint that would prompt the building supervision to take action.