https://wccftech.com/ios-13-installed-on-50-of-all-iphones-ipados-on-33-of-all-ipads-apple/

Apple's latest mobile operating system updates have been installed on almost half of the device user base. iOS 13 has been installed on 50% of all compatible iPhones, while iPadOS has been installed on 33% of all compatible iPads.

Apple released these numbers on their developer website, where they updated the numbers on October 15. These numbers are measured by Apple from the App Store and used to inform developers on the operating systems that they should support with their apps.