I had a problem with this a while back. I solved it by going into System Preferences, Sharing, File Sharing and specifically adding my Music Library folder to the list of shared folders.

It’s really stupid that a Sonos upgrade broke this but c’est la vie.

I know there are a couple people who have written very in-depth HOW-TOs on fixing it on this forum because you are definitely not the first person to suffer this “feature upgrade” or whatever one wants to call it.

Thank you but I have already tried this and still no luck