I have a MacBook, two Airport Express devices, a SoundBar with AirPlay ability, and a bluetooth speaker. I want to stream this laptop's audio to all devices from any program - at a minimum all the AirPlay devices.
Through iTunes (still running High Sierra on this MacBook) I can select all AirPlay devices, and this works great:
Using the Audio MIDI Setup program I can also set up a Multi-Output Device which plays audio via the MacBook and the Bluetooth speaker:
I am quite happy with just the AirPlay devices, but this only works via iTunes. As I play most of my music through YouTube Music these days, I am wondering if there is any program that will let me send the computer's audio to all AirPlay devices in this way? And if possible, to the bluetooth speaker also would be amazing.