“Do Not Track” (DNT) is a simple HTTP header that a browser can send to
signal to a web site that the user does not want to be tracked. The DNT
header had a promising start and the support of major browsers almost a decade
ago. Most web browsers still support sending it, but in 2020 it is almost
useless because the vast majority of web sites ignore it. Advertising
companies, in particular, argued that its legal status was unclear, and
that it was difficult to determine how to interpret the header. There have
been some relatively recent attempts at legislation to enforce honoring the
DNT header, but those efforts do not appear to be going anywhere. In
comparison, the European Union’s General
Data Protection Regulation (GDPR) and the California
Consumer Privacy Act (CCPA) attempt to solve some of the same problems
as DNT but are legally enforceable.

Source: LWN.net – [$] The sad, slow-motion death of Do Not Track