My system was fully updated. (Microsoft forces it down your throat whether you like it or not).
I was having an error doing an "override the system". I ran SFC /SCANNOW, DISM, etc... everything was coming back good, but Windows 11 insisted I was running VIrtualBox. I was not. Not at any time. It was not pre-loaded by the manufacturer of the PC either....
Microsoft should not refuse to "override" an OPERATING SYSTEM (their operating system..) because of an APPLICATION..... completely preposterous. Anyways...
So, I downloaded a brand new official image from Microsoft, and installed Windows 11 Pro, fresh. Version 21H2 Build 22000.856. All updates are applied.
With base "functional" computer, it behaves as I described in my original post.
With all drivers and core programs installed (latest RTX3080 Nvidia etc), it behaves as I described in my original post.
Installing Chrome, Firefox, Brave, tried all three (along with Edge each time), and it behaves as I described above.
I read this post: https://answers.microsoft.com/en-us/windows/forum/all/disabling-under-prioritization-of-background-tasks/c4749a47-76f0-4c5c-bb30-b9d319f610fc
I sincerely do not comprehend how you can indicate you've tested my scenario and not have experienced the same issue. Please test it. I question your claim because it seems rather uncommon that someone cares about a video stream running ***in the background*** and you can't know if its doing so unless you are running another application to monitor it, or specifically looking at the behaviors when you wake the window back up.
I then ran Hyper-V and created a Win8.1 system **on this pc** installed Firefox & Chrome, and ran the same test and it works perfectly fine when I have other windows fully maximized inside of the VM. HOWEVER< on this machine it does not work when running it on the core Windows 11 OS.....
Which goes back to my original claim..... Microsoft is messing with system resources when a video is known to be "invisible" to the user......