This contains a fix for SUPPORT-288 which was suggested by Raymond Chen here: https://devblogs.microsoft.com/oldnewthing/20200302-00/?p=103507

GreenshotPlugin/Core/WindowsEnumerator.cs

@@ -0,0 +1,114 @@
+/*
+ * Greenshot - a free and open source screenshot tool
+ * Copyright (C) 2007-2020 Thomas Braun, Jens Klingen, Robin Krom
+ *
+ * For more information see: http://getgreenshot.org/
+ * The Greenshot project is hosted on GitHub https://github.com/greenshot/greenshot
+ *
+ * This program is free software: you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation, either version 1 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program.  If not, see <http://www.gnu.org/licenses/>.
+ */
+
+using GreenshotPlugin.UnmanagedHelpers;
+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace GreenshotPlugin.Core {
+    /// <summary>
+	/// EnumWindows wrapper for .NET
+	/// </summary>
+	public class WindowsEnumerator {
+		/// <summary>
+		/// Returns the collection of windows returned by GetWindows
+		/// </summary>
+		public IList<WindowDetails> Items { get; private set; }
+
+		/// <summary>
+		/// Gets all top level windows on the system.
+		/// </summary>
+		public WindowsEnumerator GetWindows() {
+			GetWindows(IntPtr.Zero, null);
+			return this;
+		}
+
+		/// <summary>
+		/// Gets all child windows of the specified window
+		/// </summary>
+		/// <param name="parent">Window Handle to get children for</param>
+		public WindowsEnumerator GetWindows(WindowDetails parent)
+		{
+			GetWindows(parent?.Handle ?? IntPtr.Zero, null);
+			return this;
+		}
+
+		/// <summary>
+		/// Gets all child windows of the specified window
+		/// </summary>
+		/// <param name="hWndParent">Window Handle to get children for</param>
+		/// <param name="classname">Window Classname to copy, use null to copy all</param>
+		public WindowsEnumerator GetWindows(IntPtr hWndParent, string classname) {
+			Items = new List<WindowDetails>();
+			IList<WindowDetails> windows = new List<WindowDetails>();
+			User32.EnumChildWindows(hWndParent, WindowEnum, IntPtr.Zero);
+
+			bool hasParent = !IntPtr.Zero.Equals(hWndParent);
+			string parentText = null;
+			if (hasParent) {
+				var title = new StringBuilder(260, 260);
+				User32.GetWindowText(hWndParent, title, title.Capacity);
+				parentText = title.ToString();
+			}
+
+			foreach (var window in Items) {
+				if (hasParent) {
+					window.Text = parentText;
+					window.ParentHandle = hWndParent;
+				}
+				if (classname == null || window.ClassName.Equals(classname)) {
+					windows.Add(window);
+				}
+			}
+			Items = windows;
+			return this;
+		}
+
+        /// <summary>
+		/// The enum Windows callback.
+		/// </summary>
+		/// <param name="hWnd">Window Handle</param>
+		/// <param name="lParam">Application defined value</param>
+		/// <returns>1 to continue enumeration, 0 to stop</returns>
+		private int WindowEnum(IntPtr hWnd, int lParam)
+        {
+            return OnWindowEnum(hWnd) ? 1 : 0;
+        }
+
+        /// <summary>
+		/// Called whenever a new window is about to be added
+		/// by the Window enumeration called from GetWindows.
+		/// If overriding this function, return true to continue
+		/// enumeration or false to stop.  If you do not call
+		/// the base implementation the Items collection will
+		/// be empty.
+		/// </summary>
+		/// <param name="hWnd">Window handle to add</param>
+		/// <returns>True to continue enumeration, False to stop</returns>
+		protected bool OnWindowEnum(IntPtr hWnd) {
+			if (!WindowDetails.IsIgnoreHandle(hWnd)) {
+				Items.Add(new WindowDetails(hWnd));
+			}
+			return true;
+		}
+	}
+}