How did you install the Channels DVR Server docker container?
docker run command line?
docker compose statement?
Show us the docker run statement you used, or the docker compose statement you used.
If you understand docker, like you say you do, you should understand volume mappings and how they work.
You have Channels DVR recording to /root/ganar
in the Channels DVR docker container.
Where did you volume map that to on your NAS?
You're also using a bridge network for the container instead of host network. You probably can't see the Channels DVR Server with any Channels client app because of that.