MacOS - how to write a utility to run in the background?

Question

C++ / C#

Greetings.
I am an absolute noob. I recently learned C++, before that I was in Python, I wrote in JS/PHP for a very long time. That is, I have no experience in system programming.
The task arose - to make one utility for working in the background. I understand in principle how, but there are a lot of nuances - how to register a service and run it? How to hang its icon in the menu bar and add a settings window? And most importantly - how to debug all this, because in the playground this will not start?
The question is not idle - the courses reviewed by me describe the creation of window applications "in themselves". Interaction with the system, if described, is very brief and not detailed.
I would be grateful for a tip on the materials that will allow you to quickly get up to speed, even in general terms.

Answer 1

Info.plist:
LSUIElement = YES
AppDelegate.swift:

import Cocoa

@NSApplicationMain
class AppDelegate: NSObject, NSApplicationDelegate {
    let statusMenu: NSMenu = .init()
    let statusItem = NSStatusBar.system.statusItem(withLength: NSStatusItem.squareLength)

    func applicationDidFinishLaunching(_ aNotification: Notification) {
        
        statusItem.button?.image = NSImage.init(named: NSImage.actionTemplateName)
        statusItem.menu = statusMenu
        
        let quitMenuItem: NSMenuItem = .init(title: "Quit", action: #selector(quit), keyEquivalent: "")
        statusMenu.addItem(quitMenuItem)
    }
    
    @objc func quit() {
        NSApp.terminate(self)
    }
}

The rest is in the courses.