Planning of the technical room (distance between devices)

I would ask the electrician what size of the control cabinet is necessary. Often they install much too large boxes that no one needs and that just take up unnecessary space on the wall. Unfortunately, that happened to me. Huge, unnecessarily expensive, and empty inside! The cable ducts also looked as if they had been dragged behind a truck. It's "only" the utility room, but still, you don't have to accept everything and let them install what the technician has "forgotten" for years in the furthest corner of the warehouse.

I can only understand parts of it, usually there are complaints about it being too small when something needs to be retrofitted.

Basically, you have 1-x rows for the meter, nothing should really be installed above that (upper connection compartment), next to it there is usually an APZ field installed today (in the vast majority of cases empty), above that fuses, RCDs, etc. can be installed. Additionally, about 30% space for expansions should actually be provided. That would be the absolute minimum and 55cm wide; one more row, so 80cm for a simple single-family house with 1 meter without anything special would be the absolute minimum for me to be able to accommodate a few RCDs, fuses, etc. sensibly. With photovoltaics, battery storage, maybe a roller shutter control, use of terminal blocks, etc., I would probably go to 1m width.

Side notes, do not include the network in the electrical cabinet, it is expensive, takes up unnecessary space... Better use a simple patch panel and then house the switch/Fritzbox in a small cabinet under the ceiling for little money.

that could have been done much smaller as well....

I'm afraid I have to disagree with you :( The electrician could not have made it smaller while complying with the current requirements from the utility provider.

Below the meters are the busbars (yellow-green), so that area is full, above the meters (red) is the upper connection compartment. He is actually only allowed to install the main fuse and outgoing lines there. The black area is mostly the empty APZ field (for smart meters or similar), and just the visible installations on the left could still have fit into the second row from the left without a planned expansion space; there might also be distributor terminals or similar there that are not visible.

ah ok, thanks for the clarification.
Still, I don’t understand how it was possible to save significantly more space with other new builds using the same technology and a much smaller utility room :(

Side notes, do not place the network equipment inside the electrical cabinet, it’s expensive and takes up unnecessary space... Better a simple patch panel and then place the switch/FritzBox in a small cabinet under the ceiling for little money.

That’s a good tip, but I don’t quite understand why you want to insert a switch between the router and the end devices again. Usually, every router can handle that from the start. Or do you mean because of the possibly too many end devices (if the router only has 4 ports)?