AppKit is still dominant on macOS (despite the addition of Catalyst), UIKit is the chief framework on iOS/iPadOS/tvOS/visionOS, SwiftUI is native on watchOS and mostly wraps AppKit/UIKit on the other platforms. macOS is oriented around KB+mouse usage, iOS/iPadOS/watchOS are touch-dominant, tvOS is made to be remote-friendly, and visionOS is oriented around eye navigation and hand gestures.
macOS is far more complex and flexible than the iOS family of OSes (which are really all just iOS, including iPadOS).
Apple claimed they were running OSX back at the iPhone launch, but it was truly very stripped down to accommodate the underpowered hardware, and they've only made incremental, very targeted expansions in the last 16 years.
