Distance from terrace to property boundary

That is unfortunately not quite correct.
If the original terrain already had a slope so that the water flows to the neighbor, and nothing is changed about the slope, then one is also not obligated to keep the water on one's own property.
Only if one makes changes to the original topography is one responsible for ensuring that the change does not burden the neighbors.

Yes, he is. The neighbor raised the terrain. That is obvious. And exactly the point of contention.

Yes, indeed. The neighbor has just raised the terrain. That is obvious.

Even if something appears obvious in photos, one must be able to prove it.

As Escroda has already written, measurements must first be taken and the neighbor’s building documents reviewed before continuing to speculate here.

The legal situation has now been sufficiently explained to the original poster.

I would, together with the neighbor, measure the height difference from the edge of the street to the neighbor's terrace using a straightedge and a spirit level. If one has a hose level or leveling instrument, even better. But the spirit level is also quite accurate. Since the property boundary in the original terrain has hardly any slope, the result is exactly what the neighbor has filled in. I would be interested in the result.

Even if something seems obvious in photos, you have to be able to prove it. As Escroda already wrote, you first have to take measurements and inspect the neighbor's construction documents before continuing to speculate here.

Access to the construction file will not be granted to you. Except from the neighbor himself? You can also determine it yourself, see above.

Within a short time, there will be a 2m privacy screen anyway, unless the women are best friends, then everything belongs to everyone

You will not be granted access to the building file.

As a neighbor, you can also request access to the building file from the building regulatory authority.
You must prove a legitimate interest for this. This would generally be affirmed if your neighborhood rights could be violated. The most common case for this is current construction procedures.

You could therefore request access in writing by stating the legitimate interest.
Alternatively, you could have the neighbor issue you a permission for access.
According to the statements of the original poster, the neighbor claims not to have changed the original topography and therefore should not fear the file inspection.
This could at least be used as an argument.