A workaround to take screenshots under macOS when Gtk# crashes doing the same (https://github.com/mono/gtk-sharp/issues/236)

MacOSScreenshot.cs

using System;
using System.Runtime.InteropServices;
using AppKit;
using CoreGraphics;
using Foundation;
using ImageIO;
using MobileCoreServices;

namespace ScreenshotDemo
{
    // NOTE Follow https://docs.microsoft.com/es-es/xamarin/mac/app-fundamentals/console to include Xamarin.Mac head-less dependencies
    public static class MacOSScreenshot
    {
        private const string _appServicesPath = 
            "/System/Library/Frameworks/ApplicationServices.framework/Versions/Current/ApplicationServices";

        // https://developer.apple.com/documentation/coregraphics/1454603-cggetactivedisplaylist
        [DllImport(_appServicesPath, EntryPoint = "CGGetActiveDisplayList")]
        private static extern int CGGetActiveDisplayList(int maxDisplays, int[] activeDisplays, out int displayCount);

        // https://developer.apple.com/documentation/coregraphics/1455691-cgdisplaycreateimage
        [DllImport(_appServicesPath, EntryPoint = "CGDisplayCreateImage")]
        private static extern /* CGImageRef */ IntPtr CGDisplayCreateImage(int displayId);

        // Based on: https://stackoverflow.com/a/40864231
        public static void Take()
        {
            NSApplication.Init();

            var result = CGGetActiveDisplayList(0, null, out int displayCount);

            // https://developer.apple.com/documentation/coregraphics/cgerror/success
            if (result != 0)
            {
                Console.WriteLine("Error retrieving the displays count.");
                return;
            }

            var allocated = displayCount;
            // CGDirectDisplayID is an Int32: https://developer.apple.com/documentation/coregraphics/cgdirectdisplayid
            var activeDisplays = new int[allocated]; // UnsafeMutablePointer<CGDirectDisplayID>.allocate(capacity: allocated)
            result = CGGetActiveDisplayList(displayCount, activeDisplays, out displayCount);

            if (result != 0)
            {
                Console.WriteLine("Error retrieving the displays list.");
                return;
            }

            for (int i = 0; i < displayCount; i++)
            {
                var handle = CGDisplayCreateImage(activeDisplays[i]);
                var screenShot = new CGImage(handle);
                //let bitmapRep = NSBitmapImageRep(cgImage: screenShot)
                //let jpegData = bitmapRep.representation(using: NSBitmapImageFileType.JPEG, properties: [:])!
#if DEBUG
                Save(screenShot, $"/Users/marcos/Desktop/screenshot-{i}");
#endif
            }
        }

        // It returns 1x1 px screenshots :-S
        // Based on: https://stackoverflow.com/q/45714609
//        public static void Take()
//        {
//            var screens = NSScreen.Screens;

//            for (int i = 0; i < screens.Length; i++)
//            {
//                var item = screens[i];
//                var screenshot = CGImage.ScreenImage(i, item.Frame);
//#if DEBUG
//                Save(screenshot, $"/Users/marcos/Desktop/screenshot-{i}");
//#endif
        //    }
        //}

#if DEBUG
        private static void Save(CGImage screenshot, string filename)
        {
            var imageFormat = UTType.PNG;
            var fileURL = new NSUrl($"{filename}.{imageFormat.ToString().ToLowerInvariant()}", false);

            using (var dataConsumer = new CGDataConsumer(fileURL))
            {
                var imageDestination = CGImageDestination.Create(dataConsumer, imageFormat, 1);
                imageDestination.AddImage(screenshot);
                imageDestination.Close();
            }
        }
#endif
    }
}