Setting aside how much worse the Music.app interface is in Tahoe, I have been having more trouble with volume control over Airplay recently. We routinely broadcast from Music.app to 2 HomePod Mini’s and a Belkin SoundForm, and a couple of times per week when we start the music playing, the volume is not what we last set it to, and adjusting the sliders in the Remote app on an iPhone doesn’t work at all (ie: the slider moves but the volume doesn’t change on any of the speakers). Even changing the volume in Music.app on the Mac doesn’t change the volume. Usually disabling the broadcast to some or all of the speakers and adding them back makes their volume controls work, but I feel like at least once even that didn’t work.
I have also seen Music forget to send output to Airplay when freshly started (it used to remember this well) or when it hasn’t been playing for a while (eg: overnight).
I tire of trying to make Music.app work well and would love to find a solid replacement, but it seems extremely rare for any app to be able to broadcast to multiple Airplay speakers at once (I don’t want to route all system audio to all our Airplay speakers; that would make beeps and the like very annoying).
I have a large music library on an external drive. And have started to use my Plex server to stream music to my Homepods. No problems doing that. On my iPad I use “Plexamp”.