Apple's ITP is creating ghost audiences; it's getting worse, and there's no cure.
A quick primer for you, without getting into the technical specifics:
Around 50% of your mobile visitors are ghosts.
Around 10% of your desktop visitors are ghosts.
That means 20%-30% of all visitors are ghosts.
Did that get your attention?
ITP or Intelligent Tracking Prevention is Apple Safari's ability to stop cross-domain tracking (specifically ad tracking), deleting or blocking cookies (1st and 3rd), with the intention of protecting user privacy by restricting the ability of ad tech companies to track people around the web.