Music won't play through Bluetooth speakers on MacBook Air

On my M2 MacBook Air (2022) running Sonoma 14.6.1, I'm playing music using the Apple Music App. The source of the music is Home Sharing from an iMac that I use as a music server. No sound comes from the bluetooth speakers — and I've tried two different sets of speakers.

The following all work fine:

1. Playing the same music (from the server) through the MacBook's built in speakers, and through the speakers on a Thunderbolt display.
2. Playing music over Bluetooth using the Music App when the source of the music is my local disk, rather than a Home Sharing server.
3. Playing sound from the MacBook through the bluetooth speakers from another app, such as Zoom.
4. Playing the same music (from the server) on an iPad, both using bluetooth speakers and the iPad's internal speaker.

I this another case of Apple breaking Home Sharing?

[Re-Titled by Moderator]