My first thought is that many if not all modern CPUs have a separate master CPU within it (such as Intel's Management Engine) that can run even when the PC is turned off.
It runs when your computer is asleep, while it’s booting up, and while your operating system is running. It has full access to your system hardware, including your system memory, the contents of your display, keyboard input, and even the network. https://www.howtogeek.com/334013/intel-management-engine-explained-the-tiny-computer-inside-your-cpu/
Could this be what is happening?
It makes me wonder, with all the legislation being drafting in Western nations, why no privacy laws stating manufacturers can't put embedded corporate spy devices in the devices they sell you? Strange isn't it.
It may have started to do an update. My old computer is not on line and won't do updates because it's outdated, that computer had that problem until it fell out of service. I like it because I have a full MS suite that I can use and transfer files with a thumb drive if I need to share them. It has no camera and no wifi
I don't use Windows. I'm going to run a few more experiments to test it out.