Highly recommend beginning with Swift and using SwiftUI for UI development. Dive into AppKit and Obj-C when (if) necessary. As an additional companion, check out the HIG [1] or Human Interface Guidelines. It's a great starting point for introducing a feature "the Apple way", and it'll make knowing what to reach for in SwiftUI much more straight forward.

[1] https://developer.apple.com/design/human-interface-guideline...