I have the following situation:
I have a server, where I have a directory of all my pictures. In my home network I serve those and other directories via NFS/Samba.
However I also want to serve the same folder over nextcloud for my remote devices.
Is this possible (without having duplicate files on the server)?
Yes it is. An admin can mount Samba drives or allow users to do it by themself. Use the “external storage” feature to mount the folders, or fix the NFS share on the operating system level and mount it with the “local” option.
There is a caveat to keep in mind. Nextcloud will not automatically scan these locations for new files, so you need to trigger a scan job by cron, or live with the performance penalty that comes with having Nextcloud scan the folder upon access.