Open a view in another window - SwiftUI for Mac

ContentView.swift

import SwiftUI

struct ContentView: View {
  var body: some View {
    Button("Open Secondary Window") {
      openSecond()
    }
    .frame(width: 400, height: 150)
  }

  // open the sub view in a new window
  func openSecond() {
    // create a hosting controller to hold the SwiftUI view
    let hostingController = NSHostingController(rootView: SubWindowView())

    // create a window to hold the hosting controller & set its title
    let window = NSWindow(contentViewController: hostingController)
    window.title = "Secondary Window"

    // create a window controller to own the window
    let controller = NSWindowController(window: window)

    // tell the controller to show the window
    controller.showWindow(nil)
  }
}

struct SubWindowView: View {
  // you must set a frame for the secondary window here
  // this uses width & height, but you'll probably want to use the full frame modifier
  var body: some View {
    Text("This is the sub window view.")
      .frame(width: 200, height: 150)
  }
}