one thing this doesn't touch on that I am curious about is how was browsing history, etc, correlated to the GDID?

Wasn't this the GUID (Globally Unique Identifier) of early 00s Windows? When did it change to GDID? Are they the same?

this is why Microsoft is pushing so hard for Microsoft accounts at install

For those like me who were not abreast of this issue: the FBI was able to arrest some kid who hacked/is alleged to have hacked a jewellery retailer through a VPN. They were able to track the hacker via the user's GDID, which is a stable identifier unaffected by VPN usage.

This surveillance is certainly going to expand in scope as age verification comes into widespread usage. Personally I see little legitimate use case for this telemetry. It seems only useful for the purposes of tracking users for law enforcement or targeted advertising purposes.

  cat /etc/machine-id

How a Windows device's global ID is generated may be new info in the public sphere, but the fact that the global ID exists is not a secret. This format of device ID has been in Windows since the initial release of Windows 10 in 2015, when it was introduced as part of Windows' current telemetry subsystem. To see your device's global ID, open Windows Feedback Hub, then go to Feedback Hub Settings and look under Device Information.