I suspect the proprietary instincts of Apple’s marketing folks to be at fault here, but it may be that the Pandora code running on HomePod as my default music service needs to be more assertive/complete.
When I try to create a scene in Apple Home that plays music, more specifically a particular Pandora station, the process hits a wall when I try to “Choose Audio” and a message pops up telling me I need an Apple Music subscription/membership. Sigh…
The described image sequence follows.


Moderator Edit: Changing title for clarity