If the file path changes, you need to add the new path.
Even if the path doesn’t change, you’ll want to re-scan the libraries to make sure Plex sees them OK.
Be aware there is a bug in the latest MacOS SMB client. This can cause Plex to not see all the files stored on a NAS. The workarounds are to (a) use NFS instead of SMB, or (b) modify the /etc/nsmb.conf files.
See Plex Files Unavailable but they’re not missing for details (same thread @plexuser-69 linked).
