The vast majority of users are leaving app tracking disabled after upgrading their iPhones to iOS 14.5, according to early analysis from a data firm.
Flurry provides insights across two billion mobile devices per month and reports just 13 percent of worldwide users have actively chosen to opt into app tracking. In the US, that number drops to just four percent.
Apple launched iOS 14.5 at the end of April, which included its much talked about App Tracking Transparency feature.
First announced in 2020, it means users must give explicit permission for apps to track them across other apps and websites for advertising purposes.
The move has been criticised by Facebook which says it will have a negative impact on small businesses.
"To help people make a more informed decision, we're also showing a screen of our own, along with Apple's," wrote Dan Levy, VP Ads and Business Products for Facebook in a blog post.
The "educational screen" appears on both the Facebook and Instagram apps.
"It will provide more information about how we use personalised ads, which support small businesses and keep apps free," he wrote.
"If you accept the prompts for Facebook and Instagram, the ads you see on those apps won't change. If you decline, you will still see ads, but they will be less relevant to you."
App tracking notifications appear when first used post-installation, but can be switched off by default in the Privacy > Tracking setting.
Users are also able to see which apps have requested permission, so choices can be changed at any time.