First step would be to go to Settings, System, System Updates and Check for Updates.  You need to make sure that both the app and the system are up-to-date. 

Thank you for your help.

System is up to date, sonos app also

Sonos OS: S2
Version: 14.0 (Build 67125031)
Hardwareversion: 1.20.3.3-2.0

Hi

What controller device are you using? What OS is it using.

Where is your library located?

Please tell us more about your network. Any mesh, access points, extenders?

Win10 Desktop Controller, on the same device

What happens if you use a mobile device. Update Music Library also greyed out on mobile app?

I had the same problem: Updating the Music Library just would not work.

I took down the entire home network for about 15 minutes and when I brought it back up, album art, new music recently added to Apple music, Sonos playlists -  all work perfectly.

Hope this helps.