Hello Deadairbrusher,
Welcome to Apple Support Communities!
We want to help so you can use AirPlay to stream audio from your Mac.
Make sure you're using these steps:
"Listen to music on your favorite speakers
Get that big band sound by streaming music from your Mac to a HomePod—or two—or any other AirPlay 2-enabled speaker. On your Mac, open the Apple Music app , queue your tunes, click in the playback controls, then select a speaker. See Use HomePod with Music on Mac."
This Apple Support page has the full details for using AirPlay on your Mac: Stream audio and video from your Mac with AirPlay - Apple Support
Are you not seeing the speaker when taking these steps? Try a normal restart of all devices then testing again to further isolate the issue.
We hope this helps.
Cheers!