Apple first added the "Do not track" option to Safari in iOS 7, which sent a message to site owners and advertisers not to track their browsing activity. By tracking your activity, these third parties can create customized content that you interact with more frequently. While the feature was always on, it's no longer available in iOS 12.2 on your iPhone.
Release Notes for Safari 12.1, the app version included with iOS 12.2, states "Do Not Track" has been removed from Safari's preferences because the standard has expired just to allow third parties to fingerprint your device and use information, although it's unclear why it "expired", but one thing is certain ̵
The support for the expired Do Not Track standard has been removed to prevent its possible use as a fingerprint variable.
Do Not Tracks Utility It was entirely dependent on the third parties to whom the signal was sent because it was not a mandatory requirement -Apps, ad networks, analytics companies, plug-in providers, and other parties hiding on the web can easily ignore the signal sent by Safari to keep your browsing activity ht to pursue. This was easy for them as there was no commonly agreed DNT standard agreement. Google, Facebook and Twitter have been known to ignore DNT requests.