Issue 1:
Disapointing 😑 I was really looking forward to finally have something like this! Hope you can fix it quick

ℹ Computer information

PowerToys version: v0.23.2

PowerToy Utility: FancyZone

Running PowerToys as Admin: Yes

Windows build number: 20231.1000

📝 Provide detailed reproduction steps (if any)

Lauch FancyZones

Select a configuration in templates, or "Create new custom" in custom tab.

Click "Edit selected layout"

✔️ Expected result

I assume a configuration editor, but it was my first try.. I the grey rectangle and a glimpse of a draggable separator.

❌ Actual result

Crash and display error.

FZEditorCrashLog.txt

📷 Screenshots

Issue 2:
I got also an error. Trying to edit the custom FancyZones. FZEditorCrashLog.txt contains:

Exception

System.ComponentModel.Win32Exception: Das System kann die angegebene Datei nicht finden
Source: MahApps.Metro
TargetAssembly: MahApps.Metro, Version=2.0.0.0, Culture=neutral, PublicKeyToken=51482d6f650b2b3f
TargetModule: MahApps.Metro.dll
TargetSite: System.String GetWindowText(System.Windows.Window)
bei MahApps.Metro.Controls.WinApiHelper.GetWindowText(Window window)
bei MahApps.Metro.Automation.Peers.MetroWindowAutomationPeer.GetNameCore()
bei System.Windows.Automation.Peers.AutomationPeer.UpdateSubtree()
bei System.Windows.ContextLayoutManager.fireAutomationEvents()
bei System.Windows.ContextLayoutManager.UpdateLayout()
bei System.Windows.Interop.HwndSource.SetLayoutSize()
bei System.Windows.Interop.HwndSource.set_RootVisualInternal(Visual value)
bei System.Windows.Window.SetRootVisual()
bei System.Windows.Window.SetRootVisualAndUpdateSTC()
bei System.Windows.Window.SetupInitialState(Double requestedTop, Double requestedLeft, Double requestedWidth, Double requestedHeight)
bei System.Windows.Window.CreateSourceWindow(Boolean duringShow)
bei System.Windows.Window.ShowHelper(Object booleanBox)
bei FancyZonesEditor.MainWindow.EditLayout_Click(Object sender, RoutedEventArgs e)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bei System.Windows.Controls.Primitives.ButtonBase.OnClick()
bei System.Windows.Controls.Button.OnClick()
bei System.Windows.Controls.Primitives.ButtonBase.OnMouseLeftButtonUp(MouseButtonEventArgs e)
bei System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.ReRaiseEventAs(DependencyObject sender, RoutedEventArgs args, RoutedEvent newEvent)
bei System.Windows.UIElement.OnMouseUpThunk(Object sender, MouseButtonEventArgs e)
bei System.Windows.RoutedEventArgs.InvokeHandler(Delegate handler, Object target)
bei System.Windows.RoutedEventHandlerInfo.InvokeHandler(Object target, RoutedEventArgs routedEventArgs)
bei System.Windows.EventRoute.InvokeHandlersImpl(Object source, RoutedEventArgs args, Boolean reRaised)
bei System.Windows.UIElement.RaiseEventImpl(DependencyObject sender, RoutedEventArgs args)
bei System.Windows.UIElement.RaiseTrustedEvent(RoutedEventArgs args)
bei System.Windows.Input.InputManager.ProcessStagingArea()
bei System.Windows.Input.InputManager.ProcessInput(InputEventArgs input)
bei System.Windows.Input.InputProviderSite.ReportInput(InputReport inputReport)
bei System.Windows.Interop.HwndMouseInputProvider.ReportInput(IntPtr hwnd, InputMode mode, Int32 timestamp, RawMouseActions actions, Int32 x, Int32 y, Int32 wheel)
bei System.Windows.Interop.HwndMouseInputProvider.FilterMessage(IntPtr hwnd, WindowMessage msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei System.Windows.Interop.HwndSource.InputFilterMessage(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei MS.Win32.HwndWrapper.WndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam, Boolean& handled)
bei MS.Win32.HwndSubclass.DispatcherCallbackOperation(Object o)
bei System.Windows.Threading.ExceptionWrapper.InternalRealCall(Delegate callback, Object args, Int32 numArgs)
bei System.Windows.Threading.ExceptionWrapper.TryCatchWhen(Object source, Delegate callback, Object args, Int32 numArgs, Delegate catchHandler)
bei System.Windows.Threading.Dispatcher.LegacyInvokeImpl(DispatcherPriority priority, TimeSpan timeout, Delegate method, Object args, Int32 numArgs)
bei MS.Win32.HwndSubclass.SubclassWndProc(IntPtr hwnd, Int32 msg, IntPtr wParam, IntPtr lParam)
bei MS.Win32.UnsafeNativeMethods.DispatchMessage(MSG& msg)
bei System.Windows.Threading.Dispatcher.PushFrameImpl(DispatcherFrame frame)
bei System.Windows.Application.RunDispatcher(Object ignore)
bei System.Windows.Application.RunInternal(Window window)
bei FancyZonesEditor.App.Main()

Environment

Command Line: "C:\Program Files\PowerToys\modules\FancyZones\FancyZonesEditor.exe" 0_0_3840_1560 "15216"

Timestamp: 10/01/2020 07:26:54

OS Version: Microsoft Windows NT 6.2.9200.0

IntPtr Length: 8

x64: True

CLR Version: 4.0.30319.42000

Assemblies - FancyZonesEditor.exe

FancyZonesEditor, Version=0.23.0.0, Culture=neutral, PublicKeyToken=null (C:\Program Files\PowerToys\modules\FancyZones\FancyZonesEditor.exe)

System.Text.Json, Version=4.0.1.2, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51 (C:\Program Files\PowerToys\modules\FancyZones\System.Text.Json.dll)

System.Memory, Version=4.0.1.1, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51 (C:\Program Files\PowerToys\modules\FancyZones\System.Memory.dll)

System.Runtime.CompilerServices.Unsafe, Version=4.0.6.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a (C:\Program Files\PowerToys\modules\FancyZones\System.Runtime.CompilerServices.Unsafe.dll)

System.Buffers, Version=4.0.3.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51 (C:\Program Files\PowerToys\modules\FancyZones\System.Buffers.dll)

System.Numerics.Vectors, Version=4.1.4.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a (C:\Program Files\PowerToys\modules\FancyZones\System.Numerics.Vectors.dll)

System.ValueTuple, Version=4.0.3.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51 (C:\Program Files\PowerToys\modules\FancyZones\System.ValueTuple.dll)

MahApps.Metro, Version=2.0.0.0, Culture=neutral, PublicKeyToken=51482d6f650b2b3f (C:\Program Files\PowerToys\modules\FancyZones\MahApps.Metro.dll)

ControlzEx, Version=4.0.0.0, Culture=neutral, PublicKeyToken=69f1c32f803d307e (C:\Program Files\PowerToys\modules\FancyZones\ControlzEx.dll)

ManagedCommon, Version=0.23.0.0, Culture=neutral, PublicKeyToken=null (C:\Program Files\PowerToys\modules\FancyZones\ManagedCommon.dll)

Telemetry, Version=0.23.0.0, Culture=neutral, PublicKeyToken=null (C:\Program Files\PowerToys\modules\FancyZones\Telemetry.dll)

Microsoft.Xaml.Behaviors, Version=1.1.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a (C:\Program Files\PowerToys\modules\FancyZones\Microsoft.Xaml.Behaviors.dll)

mscorlib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\Windows\Microsoft.NET\Framework64\v4.0.30319\mscorlib.dll)

System, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System\v4.0_4.0.0.0__b77a5c561934e089\System.dll)

System.Core, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Core\v4.0_4.0.0.0__b77a5c561934e089\System.Core.dll)

PresentationFramework, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\PresentationFramework\v4.0_4.0.0.0__31bf3856ad364e35\PresentationFramework.dll)

WindowsBase, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\WindowsBase\v4.0_4.0.0.0__31bf3856ad364e35\WindowsBase.dll)

PresentationCore, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 (C:\WINDOWS\Microsoft.Net\assembly\GAC_64\PresentationCore\v4.0_4.0.0.0__31bf3856ad364e35\PresentationCore.dll)

System.Xaml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Xaml\v4.0_4.0.0.0__b77a5c561934e089\System.Xaml.dll)

System.Configuration, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Configuration\v4.0_4.0.0.0__b03f5f7f11d50a3a\System.Configuration.dll)

System.Xml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Xml\v4.0_4.0.0.0__b77a5c561934e089\System.Xml.dll)

PresentationFramework.Aero2, Version=4.0.0.0, Culture=neutral, PublicKeyToken=31bf3856ad364e35 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\PresentationFramework.Aero2\v4.0_4.0.0.0__31bf3856ad364e35\PresentationFramework.Aero2.dll)

PresentationFramework-SystemXml, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\PresentationFramework-SystemXml\v4.0_4.0.0.0__b77a5c561934e089\PresentationFramework-SystemXml.dll)

System.Windows.Controls.Ribbon, Version=4.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\System.Windows.Controls.Ribbon\v4.0_4.0.0.0__b77a5c561934e089\System.Windows.Controls.Ribbon.dll)

netstandard, Version=2.0.0.0, Culture=neutral, PublicKeyToken=cc7b13ffcd2ddd51 (C:\WINDOWS\Microsoft.Net\assembly\GAC_MSIL\netstandard\v4.0_2.0.0.0__cc7b13ffcd2ddd51\netstandard.dll)

mscorlib.resources, Version=4.0.0.0, Culture=de, PublicKeyToken=b77a5c561934e089 (C:\WINDO

Originally posted by @rgisler in #6877 (comment)