Whenever Sonos has a system update, they require that the Controller on macOS be updated. They provide the apparent means (click on Update) but always fail to complete the update. There is no error code, it just fails to complete. Always. The app will not proceed to play music - it insists on the update.
The way I have found to deal with this is to get Sonos tech support to send me a link to the updated .dmg (installation image). I suggest that Sonos make this readily available so I don’t have to reach out to tech support.
If you follow Support-Update Issues, it recommends to uninstall and reinstall. But, it doesn’t provide a link for reinstalling.
If you follow Support-S2, it tells you how to upgrade an S1 system to S2. That process starts with “Open the Sonos S1 Controller” for iOS or Android. 1) that reflects Sonos’ reliance on mobile apps (and negligence of desktop apps), 2) it is directions to update any devices you may still have on S1, 3) it does nothing for the desktop controller on macOS.
Sonos, please, make the macOS S2 controller app latest version readily available at your web site.