This is an Apple requirement, you are using their cloud storage and to stream from it they want you to subscribe to Apple Music.

But how can that be? I pay Apple for iCloud storage. The CDs are mine copied onto iTunes, I pay iTunes Match subs to access (my own!) music. And I can play any of my music using the Music App on iPhone or Mac, it’s just Sonos which does not appear to recognise that we have full access to our own music without paying any subs to Apple Music!!

Bizarre!

Ask Apple.  Sonos isn't the one insisting you pay, and they make no money from third party music services.

I feel this is a software problem, that Sonos does not appear to understand that you are free to play music off Apple Music, WITHOUT, a subscription, so long as it is your own ripped music! When I open the App on my phone or Mac, I am able to see & play my albums. 
When I open via Sonos, it only detects, “no subscription”. 
Sad hey

The results you get in the Sonos app are provided by Apple. If you do not see your albums it is Apple’s doing.

Maybe I misunderstand what you are trying to achieve. But I have my ripped cds in iTunes on my Mac computer and I add the iTunes music folder in the Sonos controller program on the Mac. This way I can play my whole ripped library on Sonos using the Sonos app and it is in lossless cd quality, Apple Lossless. Or are you in a situation where you don’t have access to your ripped files, only your iTunes Match files?

You can feel anything you wish, your feelings do not override the facts.  Apple is responsible for their interface in the Sonos app.  So complain to Apple.

Understand, but incredibly frustrated!

easy solution appears to be:

drop Deezer subscription

subscribe to Apple Music (similar cost)

transfer across all playlists & downloaded albums using a transfer App.

Apple has won again!

Apple provides you with a service, enabling you to upload your music to their service so you can store and play it. I do not find it strange they limit this service. To you it is free, but costs them money after all.

Just a thought: if you can play your music from Apple apps, why not Airplay to your speakers? No need for the Sonos app.

It sounds like you're having trouble playing your own ripped CDs from Apple Music through your Sonos system. While you're able to play the music directly from your iPhone or laptop, the Sonos system is giving you an error message that you need to subscribe to Apple Music. This can be frustrating, especially since you already own the music and are a subscriber to another music streaming service.

One possible explanation for this issue is that Sonos may not have access to the specific music files you're trying to play, even though they're stored in your Apple Music library. Sonos uses a different method of accessing and playing music than the Apple Music app, so it's possible that the files aren't being recognized properly.

To resolve this issue, you may want to try a few things:

1. Make sure your Sonos app is up to date. Sonos regularly releases updates to its software to fix bugs and improve performance.

2. Check your Sonos settings to ensure that your Apple Music account is properly connected. You may need to re-authenticate your account to ensure that Sonos has access to your library.

3. If the issue persists, try contacting Sonos customer support for further assistance. They may be able to help you troubleshoot the issue and find a solution.

Alternatively, if you're unable to resolve the issue with Sonos, you could try using AirPlay to stream the music directly from your iPhone or laptop to your Sonos speakers (if your speakers support AirPlay). Another option would be to use your Deezer subscription to stream music through your Sonos system instead.