Distance from property boundary with a lower neighboring plot

No, unfortunately not. The BayBo does not differentiate whether the neighboring property is lower.

Oh dear. At this point, I would invest the money in an initial consultation with a specialist lawyer for construction law and simultaneously read the state building code yourself (everything!)

Otherwise, everything has basically already been mentioned:
- A 4m porch has a building-like effect and should therefore somehow be reflected in the clearance areas
- If applicable, a development plan must be observed, which further restricts the state building code
- Written statements to the building authority should be well considered, in order not to destroy neighborly peace and to ensure that nothing disadvantageous ultimately backfires on you
- Your claims to easements or dismantling/modifications are no longer trivial in this case, so I would deal with this directly with legal assistance.

Hiring a lawyer does not mean you want to sue your neighbor. You should also consider whether you still depend on your neighbor’s goodwill somewhere (or not), and align your strategy accordingly

well, if the canopy counts as a "building," it is declared as a carport and becomes a "necessary building." It can then be placed up to 9m long right on the boundary and thus move 2 meters closer again. So he would only have to shorten 3m of his 12m by 1m, but in return, he can extend 9m by 2m.

Who now has which height is completely nonsense for the distance issues.

What you might still be able to get at is the height of his development. Because the heights of buildings on the boundary are also specified with max values from the "reference point." However, he probably has a building permit and the heights have of course been approved there.

Maybe the most sensible thing is to come to a friendly agreement with the neighbors. We also don’t know where you have shade now. A piece of the lawn at the end somewhere is "crying and annoying neighbors wherever you can," while the terrace being permanently in the shade is already bad and also drastically lowers the value of the property.

Thank you for the many replies, very kind.

I believe a lawyer is not necessary because the building authority has already stopped the construction. Because they built the roof overhang 2m too much.

Now the building authority has required the builders to create a new building plan and to obtain the approval of all neighbors by signature. I was the one who did not sign because the roof borders my property.
With the current roof overhang, there is only a naturally located boundary in the south of 0.92m (as the crow flies) and in the north of the building 2.14m, all recorded in the new building plan (which I did not sign).

As far as peace is concerned, I am not worried; the building plan has since been changed twice and I have always signed in favor of the neighbor. But eventually, everything has its limits.

He can then place it up to the border at a length of 9m and thus move 2 meters closer.

But then not with more than 3m wall height, depending on the state building code.

Yes, where is the problem? 2 meters signed and 4 meters built. What else does the office want to know? Write to them that you like FKK otherwise and that you are missing 2 meters of sun.