That is pretty unlikely and would show up in physical inspection, servicing. Also any device sold in the US with cellular access needs a FCC authorization so there isn’t any way to legally hide this in a device.
I have done a bit of research into this, and yes, with cars it’s far less regulated as those onboard computers are generally coupled with navigation technology. The companies have dubious privacy policies and there doesn’t appear to be any regulation enforcing the requirement that users not have to opt into such programs. Mozilla wrote a bit about that:
and situations like this:
It uses the “Data Communication Module (DCM)” which is not a small as you might think. This is one for Toyota, but DCMs for other cars look quite similar.
Except for the fact that WPBT isn’t supported in Linux 
So I wouldn’t say “one bit” is accurate at all.
No need for anything as complicated as that when Microsoft gives WPBT. Reflashing proprietary BIOS with a free-er one like Coreboot requires very specific hardware, and will certainly violate vendor warranties, and it is unnecessary for a user with limited experience.
There is no accurate evidence that Intel ME or other SoCs running on the mainboard are actually spying on you or a privacy risk. It is not uncommon for SoCs to have an alternative processor for out of band management and other security operations. Seeing as you mentioned Intel you can read about what AMT actually is. It’s not as scary as it sounds as it’s really meant for organizations which want to manage their devices. Most of the AMT features also not included in most laptops, except for very high end business laptops and server boards.
Link please. I doubt he has written anything saying what you wrote above.
Simply refers to things like Secure Boot, etc. See Trusted Computing for actual information about it. It is used increase security and reduce likelihood of a rootkit tampering with the boot process, you know an actual real one not an imagined one.
Another part of it is the TPM which can be used to store encryption keys such as those for Bitlocker or LUKS. Then you only have to remember a shorter password which has hardware rate limiting preventing brute force attacks.
It will however only work on some devices so no, you can’t just throw Coreboot at the problem.
Look in your BIOS see if there is a feature that relates to WPBT. It may not be entirely obvious. Reinstall windows with that feature disabled. The only other viable alternative is to build windows media with the registry key that disables it.