Seems like you're not the only one with this problem. Looks like Windows will create a display for any HDMI connection, even if you don't intend to use it.

What about running your HDMI cable from the computer to the A/V receiver, then, the receiver's HDMI output back to your computer monitor via yet another HDMI cable? That way you end up actually using the display. This could be thwarted if the A/V receiver does bad stuff to get in your way, like, limiting the resolution or refresh rate of the video signal.

Another option is, if you're only using a single monitor anyway, you can go ahead and let Windows create the display and then select "duplicate displays".

Another option I saw was to go ahead and let Windows make a display, but do the desktop arrangement, so that it's moved over down to like the lower left corner, so that your mouse is less likely to end up down there. And then hope that none of your desktop icons ever scootch down there. (And possibly use some other software to lock the mouse away from that desktop.)

Others have talked about disabling Pin 19 on the HDMI connector, but then others report that that doesn't solve all the problems.

Another option is something in this category (I don't know if this one is any good), which will extract the audio from the HDMI and send it out on a couple of different digital formats like optical and digital coaxial (if you have that as an option): https://www.monoprice.com/Product?c_id=1...=1&format=2 - This will still create a display, but you could put it inline behind the monitor and then you'd be running only one cable to the AV receiver instead of two.

I don't think ARC helps you in this case ( https://www.tomsguide.com/us/hdmi-arc-faq,news-26262.html ).

Anyway, some links:

https://hardforum.com/threads/is-there-a-way-to-output-sound-by-hdmi-without-video.1896250/
https://forums.tomsguide.com/threads/how-to-output-only-sound-through-hdmi.378729/