On December 3, 2021, Apple finished the review of version 15.1.0 of PDF Notes S & PDF Notes C and they became Ready for Sale.
On December 2, 2021, I uploaded version 15.1.0 of PDF Notes S & PDF Notes C to App Store
PDF Notes S https://itunes.apple.com/app/id961336139
PDF Notes C https://itunes.apple.com/app/id1459073729
This version supports iOS 15.