Thank you for your answers.
The neighbor is not our problem, it is the building authority. If the neighbor now plants a hedge in front of his fence, he would be practically adjoining us, at least one could argue that way. The hedge on the boundary alone would be allowed.
The problem is rather that we both would prefer to have the fence, but because of the building authority the hedge has to be in between. The landscaper left 50 cm of distance to the public area for the hedge. If you take the development plan literally, you could now plant a hedge on each side of the boundary or a hedge on the boundary, and both then place the fence in front of it. In the end, fence, 60 cm hedge, fence. That would of course be completely illogical, which the whole thing actually is anyway, since the whole area is fenced off anyway and is no longer visible from outside.
The hedge can only be maintained from the outside towards the public properties. The hedge itself does not come through the fence.