So domains are recursive tree structures. So u have node com which has a bunch of nodes below it of different domains which can have sub domains etc. Its like this cos that's how DNS was designed.
Search engines gives scores to domains and pages. When u say that the content origin of ur page is some other domain the search engines will use that knowledge to adjust rating accordingly.
Say u have 2 domains site1.example.com and site2.example.com the search engine will have a rank for site1, site2, and example.com where the rating of both site1 and site2 effect the rating for example.com.
If the content origin for all federated content has the same origin say instance.fediverse.com then the rating for all federated content will be classified as part of fediverse.com and all content will be working together across all instances boosting the fediverse as a single entity.
OK let's run through some debug steps.
Test to see if samba is working by using a docker volume instead of trying to mount a file path.
If that works we can then assume its purely a file permission issue. U can check/test that by opening a shell inside the docker container and doing investigation from their.
If from the container shell u have perm issues then u will probably need to use the docker parameter to specify the user id of the container to match that of ur host or alternativly set the filesystem to match that of the container (this will lock u out of ur servers user access to the filesystem as u will no longer be owner).
If the container shell has perms to do shit in the mounted volume then it's a samba config issue. I've never done it myself but I've heard that samba is a bitch to configure.