OK, here goes another one...

I have a 3080 GPU sending video to a 49" Odyssey NEO G9 through displayport and HDMI to a Denon Atmos receiver. 

The problem I am having is that Windows sees the receiver as a monitor, and periodically windows disappear onto the second monitor when they open and the only way to get them back is to disable the Denon as the second display (or disconnect the HDMI cable from the receiver to the monitor), then close the offending apps and then reconnect the Denon. I still want an HDMI from the receiver to the monitor so I can use the Denon's GUI to change settings and passthrough signals from other sources (Firebox, Apple TV, etc). If I turn off the receiver as a display in Display Settings then no audio goes through the HDMI to the receiver. I cannot duplicate the display, because even though the receiver is capable of 8K output, it does not pass though a 5120x1440 resolution at 240 hz, and so the monitor defaults to the lower of the two resolutions (3120x1440 @ 144 hz). I don't want to use an optical connection, as it would only send a stereo signal, and I also want Atmos, DTS:X, 7.1 etc. signals to go to the receiver. I have also looked at HDMI audio extractors, but I am worried that the PC would either continue to see the Denon as a monitor or not pass through the higher fidelity signals (plus just adding more complexity and reason for something to go wrong).

I have set the resolution for the HDMI going to the receiver to 800x600 (lowest setting) and 56 hz refresh, and hoping it won't allow Windows to extend the desktop across to the Denon because of the mismatch in resolutions. It sure would be nice though it Microsoft allowed users to click a checkbox beside each display in Display Settings to allow my PC to to only send an audio signal. (or if you could even disable video in the registry. 

Let me know if anyone has another solutions, but otherwise hopefully Microsoft fixes this, as I have to think there is a growing number of non-16:9 monitors, and so anyone trying to play PC audio through their stereo is going to run into this.