It was implemented in browsers and ignored by sites. Chrome help says:
Turn "Do Not Track" on or off
When you browse the web on computers or Android devices, you can send a request to websites not to collect or track your browsing data. It's turned off by default.
However, what happens to your data depends on how a website responds to the request. Many websites will still collect and use your browsing data to improve security, provide content, services, ads and recommendations on their websites, and generate reporting statistics.
Most websites and web services, including Google's, don't change their behavior when they receive a Do Not Track request. Chrome doesn't provide details of which websites and web services respect Do Not Track requests and how websites interpret them.[1]
About the best we have browser side is a mode where all cookies are cleared at browser exit.
That's not an implementation. That's a request to sites that you visit to comply willingly. An implementation would be defensive.
It's what you would do if you had the crazy idea that a browser should be a client for the user, and only a client for the user. It should do nothing that a user wouldn't want done. The measure of a client's functionality is indistinguishable from the ability of the user to make it conform to the their desires.
It's not realistic to completely prevent tracking solely on the client-side. Every time that you interact with a server, that's an opportunity to track you. You can't prevent unless you just completely stop interacting with the server.
> About the best we have browser side is a mode where all cookies are cleared at browser exit.
No. The best we have are adblockers and scripts like consent-o-matic.
Clearing cookies does mostly clear cookies, tracking goes far beyond that. Clearing cookies has always been a red herring enabling adtech submarines like "I don’t care about cookies".
Didn't manifest v3 kinda voided all that for chrome based browser? Even brave's time in manifest v2 is timed. For that reason have switched to Firefox.
Turn "Do Not Track" on or off
When you browse the web on computers or Android devices, you can send a request to websites not to collect or track your browsing data. It's turned off by default.
However, what happens to your data depends on how a website responds to the request. Many websites will still collect and use your browsing data to improve security, provide content, services, ads and recommendations on their websites, and generate reporting statistics.
Most websites and web services, including Google's, don't change their behavior when they receive a Do Not Track request. Chrome doesn't provide details of which websites and web services respect Do Not Track requests and how websites interpret them.[1]
About the best we have browser side is a mode where all cookies are cleared at browser exit.
[1] https://support.google.com/chrome/answer/2790761