Yes, unfortunately Spotify disabled libspotify today, see Sunset of libspotify on May 16, 2022 | Spotify for Developers. There’s currently no workaround for Mopidy-Spotify.
It’s possible that if we could patch the system_information_string being used in libspotify’s ClientResponseEncrypted that might be enough. But I’m not sure if that’s possible/realisitic to do… And I don’t time to spend trying right now. Time is probably better spent moving to something based on librespot.