This is the Swift source code to accompany the article SwiftUI on macOS: Settings, defaults and About.

TemperaDriveApp.swift

import SwiftUI

@main
struct TemperaDriveApp: App {
    let theLocalTemperaDrive = TemperaDrive()
    var body: some Scene {
        Window("TemperaDrive", id: "main") {
            ContentView()
        }
        Settings {
            SettingsView()
        }
    }
}

ContentView.swift

import SwiftUI

struct ContentView: View {
    var body: some View {
        if isInited {
            VStack {
                Button("Check") {
                    theTemperaDrive?.getVolumes()
                }
                Text((theTemperaDrive?.theVolsList.joined(separator: "\n") ?? "None"))
                    .font(.largeTitle)
            }
            .padding()
            .background(.windowBackground)
        } else {
            VStack {
                Text("Waiting for results…")
                    .font(.title)
            }
            .background(.gray)
        }
            
    }
}

#Preview {
    ContentView()
}

SettingsView.swift

import SwiftUI

let unitsCelsius = "Celsius"
let unitsFahrenheit = "Fahrenheit"

struct SettingsView: View {

    var body: some View {
        TabView {
            ShowView()
                .tabItem {
                    Image(systemName: "eye")
                    Text("Show")
                }
            UnitsView()
                .tabItem {
                    Image(systemName: "thermometer.medium")
                    Text("Units")
                }
            TimerView()
                .tabItem {
                    Image(systemName: "timer")
                    Text("Timer")
                }
        }
            .frame(width: 400, height: 150)
    }
}

struct ShowView: View {
    @AppStorage("showTemps") var showTemps = true

    var body: some View {
        VStack(alignment: .leading, content: {
            Toggle("Show Temperatures and Repeat", isOn: $showTemps)
        })
    }
}

struct UnitsView: View {
    @AppStorage("tempUnits") var tempUnits = unitsCelsius
    
    var body: some View {
        Picker("Units", selection: $tempUnits) {
            Text("Celsius").tag(unitsCelsius)
            Text("Fahrenheit").tag(unitsFahrenheit)
        }
        .pickerStyle(.radioGroup)
    }
}

struct TimerView: View {
    @AppStorage("repeatTime") var repeatTime = 5.0
    
    var body: some View {
        List {
            Slider(value: $repeatTime, in: 5...305, step: 30, onEditingChanged: { print("\($0)")
            }, minimumValueLabel: Text("5"),
                   maximumValueLabel: Text("305"),
                   label: { Text("Seconds") })
            Text("Time interval = \(Int(repeatTime)) seconds")
        }
    }
}

#Preview {
    SettingsView()
}

TemperaDrive.swift

import Foundation
import SwiftUI

var isInited = false
var theTemperaDrive: TemperaDrive?

@Observable
class TemperaDrive: NSObject {
   var theVolsList = [""]
    var theTimer: Timer?
    var theTimeInterval = 30.0
   
    override init() {
        super.init()
        self.getVolumes()
        isInited = true
        theTemperaDrive = self
        theTimeInterval = UserDefaults.standard.double(forKey: "repeatTime")
        if theTimeInterval < 5.0 {
            theTimeInterval = 5.0
        } else if theTimeInterval > 305.0 {
            theTimeInterval = 305.0
        }
        if (UserDefaults.standard.bool(forKey: "showTemps")) {
            self.theTimer = Timer.scheduledTimer(withTimeInterval: self.theTimeInterval, repeats: true, block: { _ in
                self.fireTimer()
            })
        }
    }
    
    @objc func fireTimer() {
        self.getVolumes()
    }
    
    func getVolumes() {
        self.theVolsList = [""]
// …
   }
}

End of code supplement.