“The app hasn’t added support for that with Siri” when adding a song to library

I’ll be playing music via Apple Music on my HomePods (“Hey Siri play music everywhere”) and hear a song I like. I’ll say, “Hey Siri add this song to my library,” just like I’ve done for years.

But for the last few months, every single time on every one of my four HomePods, I get the response, “The app hasn’t added support for that with Siri.”

I have updated to the latest software on all HomePods, iPads and iPhones in the house. I’ve signed out of iCloud. But still: “The app hasn’t added support for that with Siri.”

Has anyone else encountered (and solved) this? Discovering and adding music is a pretty crucial feature set for speakers and streaming, so I’d really love to get to the bottom of this!