(1) Create a user on your NAS that has RW access to your media
(2) Use the following guide to mount the Samba share, providing the appropriate NAS credentials, to allow Linux user plex local RW access to your media: Linux Tips - #4 by ChuckPa
Just follow the tutorial and do not use the GUI tools. It will work. It’s as simple as that.
Btw: also make sure you have used the official installation guide:
