That depends if you’re using Zammads docker-compose or docker (standalone) version.
For docker standalone, our documentation clearly states that this is for development only and is not persistent. ( https://docs.zammad.org/en/latest/contributing/install-docker.html )
Please note that this is a non persistent storage container and all Zammad data is lost when you’re stopping the container.
And visually lives below “development” section, not installation:
As for docker-compose, all necessary steps are described here: