Never seen this offered to be set by any browsers, though.

Firefox offers it: https://support.mozilla.org/en-US/kb/global-privacy-control

They don't seem to call it GPC, but their "ask websites not to track" feature now uses it instead of GPC.

Yes ok, and Firefox was also the only browser that offered DNT, which is why it pretty much died.

It's the complete opposite. What killed DNT is Microsoft adding it to their browser and set it to true by default, pretending they cared about their users. Doing so, it was not the expression of the users anymore and so web developers ignored it, and so it died.

Sorry, that does seem like a reasonable default. This is the fault of web developers to not respect it, not Microsoft. Nice cope.

I think you’re missing the point that this caused a backlash from the ad industry / publishers that suddenly stopped recognizing these headers, otherwise it would impact their bottom line too much. Obviously it’s a good default from a user’s perspective.

It died because companies had no incentive to respect it. The writers of the GDPR could have easily added a single line saying you had to respect the DNT header, but they chose not to.

I wonder how many websites use that header as part of their fingerprint mechanism.

It's set on by default in "privacy browsers" like Brave or Zen, but off by default in most mainstream ones -- user needs to set it on explicitly via about:config