I used to work as a driver for a pizza delivery service. Back then, in autumn/winter, I cursed that there were hardly any illuminated and clearly visible house numbers from the street.
I believe there is no regulation here. Before the last ambulance, I almost threw myself. It came racing down the hill. They even overlooked the HVO car. It makes sense that a clearly visible house number is helpful. Ours is made of black metal. HVO comes directly from the town, they don’t need the number.
Asked Google. In Bavaria, it is mandatory to install one. How it is to be procured is up to the municipalities and is stated in the ordinance. So everyone is cooking their own soup again.