Where can I get the building plans?

There are regulations for electricians about where cables must run. And the heating engineer probably only has the main pipe from bottom to top, from which the radiators or underfloor heating branch off. It's no different for you than in millions of new, old, and very old apartments and houses. Besides, it's quite possible that there isn't even a plan for the electrical system (honestly: why bother?). As of 01.01.2018, the framework conditions were incorporated into the Building Code; before that, there were no regulations. They basically said: you buy a piece of house/apartment. You don't get a blueprint with a car either. Or with a TV. It was a similar way of thinking. But honestly? It's a bit annoying, but nothing more. Hundreds of thousands of renovations happen every year without plans anyway ;-)

Did you conclude a building contract for your apartment after 01.01.2018? Then you have a right to a construction description as well as to the handover of the complete planning documents.
Please contact the builder directly (and ask the administration beforehand, in case they have the documents).

Are there regulations here?