Ok, what does it generally look like?
1. Is there a development plan - yes or no?
2. Is the northern neighboring building secured by a construction burden on your property?
3. Why can the building structure not be extended to the east, possibly narrowed to accommodate the setback that is in the northern boundary?
My first ideas would be a) to extend the house to the east AND b) to obtain a deviation from the building authority, allowing you, for example, to build up to 5m distance from the existing northern side. This is usually possible, it just needs to be specifically justified. The biggest obstacle is fire protection, but if there are no windows there, it is already good in terms of fire protection. If the city agrees to this, you gain 1m at once, then there is no need to argue about 6cm of brickwork.
Best regards
Dirk Grafe