Sample mini SwiftUI ContentView which gets to values from AppStorage/UserDefaults/CFPreferences

ContentView.swift

import SwiftUI

struct ContentView: View {
  @AppStorage("greeting") private var greeting: String = ""
  @AppStorage("name") private var name: String = ""

  var body: some View {
    VStack {
      TextField("Greeting", text: $greeting)
      TextField("Name", text: $name)

      Divider()

      Text(CommandLine.arguments.description)
        .font(.footnote)
        .frame(maxWidth: 400)
    }
    .padding()
  }
}

#Preview {
  ContentView()
}

Since arguments of the format -keyname value are parsed into CFPreferences/UserDefaults/AppStorage you run the app with ArgumentTest.app/Contents/MacOS/ArgumentTest -greeting Hola -name John and the values will appear in the @AppStorage properties. You can also use UserDefaults.shared.string(forKey: "greeting") to get the value.

The basic CommandLine.argument is also available any where, if you want/need to parse the arguments yourself.