New Navigation Bar features, new UICalendarView, and UIPageControl. Pasteboard access permissions. UISheetpresentationController improvements. SFSymbols rendering modes. Self-resizing cells. UIHostingConfiguration to embed SwiftUI into UICollectionView and UITableView.
Here is a detailed summary.
How to bridge data between the legacy app and SwiftUI back and forth. How to embed SwiftUI into UICollectionView and UITableView with UIHostingConfiguration.
Here is the summary for the "Use SwiftUI With UIKit" session from WWDC22.