The new Music app in MacOS replaced the iTunes player. If you store the majority of your songs on a Synology NAS and don’t want to import them to the local computer library there is an option via the iTunes Server on Synology.
First you’ll need to install the iTunes Server app from the Synology software center.
Once the app is installed it will start indexing the folders previously tagged by the indexer for music files. You can change the share name if desired, I kept the default.
Finally, in the Music app, drop-down select the new share from the Library menu.
That’s it! You can now use the Music app (formerly iTunes) on your MacOS with the Synology NAS share without the songs being copied over to your Mac and taking up more space.
You will need to be on the same LAN for the server to appear. I still run the Synology Audio Station to access my songs when not at home.