“This process happens transparently during browser navigation in Safari Private Browsing mode, and links that the user clicks on from Mail and Messages app.”
Advertisers dodged Safari’s cookie blocking by stuffing a tracking ID into the URL. iOS 17 strips those parameters, but only in Mail, Messages and Private Browsing. Regular Safari tabs keep them. Apple hands advertisers Private Click Measurement in the same breath, so the ad business keeps its conversion numbers and Apple keeps the privacy headline.