This is a simple file you can use to bring any AppKit NSView in to the SwiftUI. Fully customizable.

NSViewForSwiftUI.swift

struct <#NSViewForSwiftUI#>: NSViewRepresentable {

    typealias TheNSView = <#The Original UIView Type#> /* e.g. NSProgressIndicator */
    var configuration = { (view: TheNSView) in }

    func makeNSView(context: NSViewRepresentableContext<ProgressIndicator>) -> NSProgressIndicator {
        TheNSView()
    }

    func updateNSView(_ nsView: NSProgressIndicator, context: NSViewRepresentableContext<ProgressIndicator>) {
        configuration(nsView)
    }
}