"Contrary to popular belief, there is no central administration of resident registration in Germany. The exception is the registration of resident aliens (see Central Register of Foreign Nationals). Registration is organized by 5283 local offices throughout Germany.[18] "

https://en.wikipedia.org/wiki/Resident_registration#Germany

I was also told something on identity cards only lives on the cards, but cannot find the source or details on that.

Each municipality is free to choose their own solution to the legal requirements (which includes a standardized API). For the moment, there are eight different software solutions on the market (developed by both public and private entities), see https://www1.osci.de/meldewesen/xmeld/registrierte-herstelle...