106rallye, and John B, you were right. I followed your advice 106rallye and spoke to a very helpful Sonos representative (in Transylvania of all places), who talked me through the relevant update. The update was to the S1 app not an upgrade to S2. Unfortunately, it was not available on my phone since the phone's OS is no longer supported by Sonos, being Android 7. Hence, I had to install the Sonos S1 app on my wife's iPad and update the system on that. The whole thing worked pretty smoothly after that. And now the system works on both my phone and my PC though I will not be able to update on either of these devices, only on the iPad or some other fully supported device.
So, you were right about this not being a conspiracy on Sonos’ part, John B, but simply part of the update churn. John B. Thanks for your advice and apologies for being dismissive of it in earlier posts.