I checked the contents of the volume specified in docker-compose.yml and it stays emtpy. I did find the database files stored in another volume that is managed by docker.

Is the line and creation of the volume db-data unnecessary and thus can be removed or is it another configuration option thats missing?

I skimmed the docs for the MySQL container (https://hub.docker.com/_/mysql) and it seems to me that there are two options for storing the data and the option where Docker manages the storage database data is used.

Any ideas on how to fix this so the data is in db-data?

I am quite new to docker and maybe I am missing something else?