Example of using NSButton in SwiftUI to access missing features like `keyEquivalent` (for example, to make the button the default and highlighted). Stack Overflow answer: https://stackoverflow.com/a/58337529/64949

NativeButton.swift

/**
```
struct ContentView: View {
	var body: some View {
		NativeButton("Submit", keyEquivalent: .return) {
			// Some action
		}
			.padding()
	}
}
```
*/
@available(macOS 10.15, *)
struct NativeButton: NSViewRepresentable {
	enum KeyEquivalent: String {
		case escape = "\u{1b}"
		case `return` = "\r"
	}

	var title: String?
	var attributedTitle: NSAttributedString?
	var keyEquivalent: KeyEquivalent?
	let action: () -> Void

	init(
		_ title: String,
		keyEquivalent: KeyEquivalent? = nil,
		action: @escaping () -> Void
	) {
		self.title = title
		self.keyEquivalent = keyEquivalent
		self.action = action
	}

	init(
		_ attributedTitle: NSAttributedString,
		keyEquivalent: KeyEquivalent? = nil,
		action: @escaping () -> Void
	) {
		self.attributedTitle = attributedTitle
		self.keyEquivalent = keyEquivalent
		self.action = action
	}

	func makeNSView(context: NSViewRepresentableContext<Self>) -> NSButton {
		let button = NSButton(title: "", target: nil, action: nil)
		button.translatesAutoresizingMaskIntoConstraints = false
		button.setContentHuggingPriority(.defaultHigh, for: .vertical)
		button.setContentHuggingPriority(.defaultHigh, for: .horizontal)
		return button
	}

	func updateNSView(_ nsView: NSButton, context: NSViewRepresentableContext<Self>) {
		if attributedTitle == nil {
			nsView.title = title ?? ""
		}

		if title == nil {
			nsView.attributedTitle = attributedTitle ?? NSAttributedString(string: "")
		}

		nsView.keyEquivalent = keyEquivalent?.rawValue ?? ""

		nsView.onAction { _ in
			self.action()
		}
	}
}



// MARK: - Action closure for controls

private var controlActionClosureProtocolAssociatedObjectKey: UInt8 = 0

protocol ControlActionClosureProtocol: NSObjectProtocol {
	var target: AnyObject? { get set }
	var action: Selector? { get set }
}

private final class ActionTrampoline<T>: NSObject {
	let action: (T) -> Void

	init(action: @escaping (T) -> Void) {
		self.action = action
	}

	@objc
	func action(sender: AnyObject) {
		action(sender as! T)
	}
}

extension ControlActionClosureProtocol {
	func onAction(_ action: @escaping (Self) -> Void) {
		let trampoline = ActionTrampoline(action: action)
		self.target = trampoline
		self.action = #selector(ActionTrampoline<Self>.action(sender:))
		objc_setAssociatedObject(self, &controlActionClosureProtocolAssociatedObjectKey, trampoline, .OBJC_ASSOCIATION_RETAIN)
	}
}

extension NSControl: ControlActionClosureProtocol {}

// MARK: -

Thanks for this code.

For my purpose I also added button.keyEquivalentModifierMask = .command to respond to to the command key as in ⌘-s .

I also added

import SwiftUI
import AppKit
import Cocoa

so I could save it in a separate file.