WIndows 11 stops recognizing monitors as audio output devices when idle

I am testing a program that for each iteration uses a unique output device (SPEAKERS / HDMI 1 / HDMI 2 / S/PDIF digital). I was experiencing the same issue with the sessions that use the HDMI monitors as sound output devices. I would kick off the test and go to bed, being awakened 30 minutes later when both of these sessions would be blasting full blast from my sound bar. and the only way to stop it was to set the output device for each of those sessions to S/PDIF or something else. I would check and the output device would be set to Default (Speakers). It finally dawned on me this morning, that when the system puts the displays to sleep, Windows decides that HDMI output device are not available and switches to Default output for those sessions.

The fix is to tell Windows to Never put your displays to sleep and use a screen saver with it set to 'blank screen'. It doesn't save power, but prevents burn-in. Yes, LCD and LED screens can have burn-in. Fortunately, it sort of self heals on my ASUS displays when something else is shown for a while, or when I shut them down. Hope this helps you.

BTW:
Does anyone know how to set the audio output device for my app (not the default audio device) from Visual C++ rather than the Windows Sound Settings?

Using IMM... .. PolicyConfig->SetDefaultDendpoint().

I got that working, but it sets the default output device instead of the one for just this session.