HDMI monitor claims it has speakers when it doesnt?

[madires]

ALSA will report an additional sound device for each HDMI port which supports sound output. It doesn't matter if there's a monitor connected to the HDMI port or if the monitort has built-in speakers. If you want to disable that sound device you can do that via the modprobe configuration for example.

[newbrain]

I have an MSO-compatible device..

Microsft Office?

What is an MSO-compatible device, google is not helping...

On the PC side:
What kind of video card are you using? Intel/AMD integrated graphics? A separate GPU? Model?
While it could be handy on a PC, I have yet to see any that supports CEC - apart, as said, the RPi*.
If you have a RPi, why not check whether you are getting CEC events from the display? I'm pretty sure you'll find none, since:
It makes almost no sense for a monitor to support CEC, as the functions are usually accessed from a remote, and that Acer does not have one.
Its manual only mention CEC in the pinout of the HDMI (but that's just the standard pinout).

On a completely different side (maybe one side of the PC):
A colleague of mine has got a new, fancy mouse. He was fading in and out of our Teams call until he realized he has a scroll wheel on the side of the mouse, and it controls the audio system!

* You can use cec-client.

[cdev]

Mixed signal oscilloscope. Its a bitscope. It does a little bit of everything. But I fixed the weird audio issue ysterday, I think. . I noticed that I only got the distracting problem when the headphones were plugged into the designated front panel headphone jack which I had abandoned using before, but then forgotten the reason. Well the reason was there was some internal breakage in the wires connecting the front panel jacks to the mother board. Its been here for years but gets forgotten. I'm using headphones a lot because my old venerable sony V6's (Which I have had and used almost continuously since the early 1990s, quite  major music-listening period for me.. broke. And te replacement I ended up with are quite decent..

After that my wife lent me a pair of Bayer DT-235s,, one of maybe a dozen pairs of nice sound blocking headphones she has bought and put aside in her search for the elusive sound she wants..  But it seems the Bayerdynamics are quite good, IMHO. surprisingly good, a $40 headphone that seems to put my ($99, but ancient) MDR-V6s to shame. Plus they have a nice, long, sturdy cord. So now I am using them with a ($5) SYBA external USB card and the combination just sounds amazing, and this weird problem has ended as long as I stay away from the borked front panel headphone jack.

[cdev]

ALSA will report an additional sound device for each HDMI port which supports sound output. It doesn't matter if there's a monitor connected to the HDMI port or if the monitort has built-in speakers. If you want to disable that sound device you can do that via the modprobe configuration for example.

or hdajackretask, which lets you remap the jacks.