I have tried to add images from (Truenas Core) network folders to my Linux desktop DT. It doesn't work. I have read other posts in this forum some of which suggest using sshfs, or NFS, and discussion on why one is better than the other, etc.
I have tried CIFS, NFS and sshfs shares and they all behave the same way. The 'import' 'add to library' dialog allows me to add a custom place (using the + button), and choose a mounted network location. When I choose the location I can browse that location's sub-folders, and eventually I choose open to add that folder location. I am returned to the 'add to library' dialog, no files are visible and the list of places includes a new place labelled (null). In the image linked below you can see I have been trying a few variations and ended up with 4x (null) folders.
DT4 import - add to library... - network mounted folders shown as (null)