Are the versions of the core different for different OS? My friend has his running on a Linux box and his storage / scan options are different than what I have on my Windows box. He can set a time interval for scanning while I cannot.
This all came about because my core isn’t added new music that I put on my NAS unless I force a scan.
Roon can’t “watch” a networked drive for changes, only a locally attached one. The work around is a manual rescan, which can be scheduled to somewhat re-automate things again.
My NUC box, with Linux and Roon Core, has an internat SSD for storing the music library, but currently the music library is still stored in my NAS. When I drop new albums in my NAS, it is not shown at once in Roon. Of course, I can manually rescan, as @mikeb says, in order to “see” those albums. But after a while (I can not say exactly how long) the new albums are available. I usually see those albums the next day, but my listening sessions are short, so my next session uses to be the next day.
In brief, eventually the new albums are available for listening without further actions. If you are in a hurry, you can manually rescan the library.
Scanning changes/additions to collections on NAS devices is known to be variable and I believe I am correct in saying a core on Linux exacerbates the problem. It isn’t a deal breaker, just be prepared to kick off a scan if you want to play the stuff immediately.