I didn’t think much of what the “correct” location would be. But i have a general kinda everything share at /var/share/[music,books,video,user folders,repo]. And then any caching or config data sits in that dockers home folder under /etc/docker/[jellyfin,immich,kavita,etc] together with its docker-compose file. All docker services run under the group user so they all have access to the share.