Ok double checked this is an error due to some misconfiguration in the part under
volumes:
in the compose.yaml file.
in this section:
volumes:
- ${USERDIR:-$HOME}/docker/music-assistant-server/data:/data/
you have to replace ${USERDIR:-$HOME}/docker/music-assistant-server/data with the correct path that you setup in the NAS.
Looking at the picture something like: /replace_with_my_path/music-assistant-server/data or similar.