MuseScore does not respect chosen audio output on MacOS
Audio generated by MuseScore should be sent to whatever audio output device is selected in the Sound output preferences dialog.
Audio generated by MuseScore appears to very strongly prefer to be sent to the MacBook laptop speakers, regardless of which output device is chosen in the sound output preferences.
I have, once, been able to somehow get MuseScore to play audio through my USB headphones. I'm not sure how. It has not happened since, and I've repeated the steps below several times. Each time since, the output from MuseScore plays out of my laptop speakers.
Steps to reproduce:
1) Open MuseScore on a MacOS platform.
2) Plug in a pair of headphones. Confirm that other audio-playing tasks (YouTube music videos, in my case) play through the headphones.
3) Bring focus to MuseScore, and play a song. Observe the audio coming from the built-in laptop speakers.
4) Open Sound preferences, switch output to MacBook Pro speakers.
5) Observe that now YouTube plays through laptop speakers. MuseScore audio continues to play through MacBook speakers.
6) Switch audio back to USB earphones.
7) Observe that YouTube video now plays through headphones. MuseScore audio continues to play through Macbook laptop speakers.
A note on "severity" value here
I've chosen "Major" because I don't want to force those around me to listen to my fiddling with a score. My wife doesn't want to hear me tweaking things endlessly, and I don't feel I can use the product when I can't direct where the sound goes. Obviously you are free to triage this bug into whatever severity you like, but if I can't control the output this will significantly restrict the time periods during which I can use this product - or even if I use it at all.