The Playbar is connected to your TV’s optical port so the TV needs to be turned on to play music streaming on the Apple TV. If you want to stream music to the Playbar with the TV turned off, stream music directly from the Sonos app instead.

OK.  I’ve figured out how to stream music from the Sonos app to the Playbar without turning the TV on.  I guess the Playbar is too old to work with Airplay 2?  The only left is to figure out how to stream podcasts.  Any advice is appreciated.  

Yes, unfortunately, the PLAYBAR was conceived, designed, and implemented long before Apple released AirPlay 2, and consequently can not be a “target” for Apple’s system.

You can, however, target another speaker in your system, and “group” the PLAYBAR with it to get the AirPlay 2 signal to play out of the PLAYBAR. Something I used to do regularly. send an AirPlay 2 signal to a Sonos One, and then group the PLAYBAR with it. 

Great idea!  Thanks.