Apple has upgraded SharePlay when dealing with Apple Music in iPadOS 18, but only when connected to supported external devices like HomePods and select speakers.
SharePlay with Apple Music gets an upgrade in iPadOS 18
Having an active SharePlay session in Apple Music no longer relies on being in a FaceTime call, iMessage chat, or CarPlay session. Apple has expanded the feature to HomePods and select speakers so participants can join in on controlling the Up Next playlist.
However, the rules and requirements for the new feature aren’t available. Anonymous sources with access to Apple’s betas have reported various results depending on the device in use.