Seems to be fixed for me with iOS 15 SDK (Xcode 13 required). Moreover, it's started to work on iOS 14 too (tested on iOS 14.5 Simulator for iPad Pro 9.7 inch, iPhone 8, iPhone 11). I recommend to test this issue again on Xcode 13 and remove workarounds if it works for you too.

Still the same on iOS 14.2

Same problem here. I made onboarding screen using collection view without any supplementary items with orthogonalScrollingBehavior = .groupPagingCentered, and scrollToItem(at:at:animated:) doesn't work on iOS 14, but works fine on iOS 13. Thanks for temporary solution with .continuousGroupLeadingBoundary, but I hope it would be fixed in iOS 14.1+