Are SwiftUI components backed by their UI-/AppKit equivalents?

As far as I know you are able to create your own wrapper around UIKit components (as can be seen in this pull-to-refresh adapation for SwiftUI).

However, I was wondering whether e.g. a SwiftUI Button is, behind the scenes, actually backed by a NSButton or UIButton respectively? Alas, I couldn't find anything in the offical documentation. Is there any statement by Apple on this matter?

Thanks in advance :)