Their usual slack style in effect here: vaguely claim “I’d like to help”, ask for more information, get given more information, then fuck off and never bother to answer again.
I have found the solution for this myself (zero thanks to Microsoft, obviously), and it appears to involve not a stupid third party program, but going to edge://flags and disabling it there, under Hardware Media Key Handling
Quite WHO thought that we would all just love an utterly needless media control overlay in the top left corner of our screens at completely random intervals needs to stop taking the nose candy and learn about computers.
The overlay of the volume control alone is still being a fucking parasite, so I’m still looking into disabling this utter nonsense too.