public class NativeWin32
 {
     [DllImport("shell32.dll")]
     public static extern int SHGetPropertyStoreForWindow(IntPtr hwnd, ref Guid riid, out IPropertyStore propertyStore);

     [DllImport("ole32.dll")]
     public static extern int PropVariantClear(ref PROPVARIANT pvar);

     // Define IPropertyStore interface
     [ComImport]
     [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
     [Guid("886D8EEB-8CF2-4446-8D02-CDBA1DBDCF99")]
     public interface IPropertyStore
     {
         void GetCount(out uint cProps);
         void GetAt(uint iProp, out PROPERTYKEY pkey);
         void GetValue(ref PROPERTYKEY key, out PROPVARIANT pv);
         void SetValue(ref PROPERTYKEY key, ref PROPVARIANT pv);
         void Commit();
     }

     // Define IID for IPropertyStore
     public static Guid IID_IPropertyStore = new Guid("886D8EEB-8CF2-4446-8D02-CDBA1DBDCF99");

     // Define PROPERTYKEY struct
     [StructLayout(LayoutKind.Sequential, Pack = 4)]
     public struct PROPERTYKEY
     {
         public Guid fmtid;
         public uint pid;

         public PROPERTYKEY(Guid fmtid, uint pid)
         {
             this.fmtid = fmtid;
             this.pid = pid;
         }
     }

     // Define PROPVARIANT structure (simplified, we'll use a simple one for bool)
     [StructLayout(LayoutKind.Explicit)]
     public struct PROPVARIANT
     {
         // We'll only implement the necessary part for boolean
         [FieldOffset(0)] public ushort vt;
         [FieldOffset(8)] public byte boolVal;

         public void SetValue(bool value)
         {
             // VT_BOOL
             vt = 11;
             boolVal = value ? (byte)1 : (byte)0;
         }
     }
 }

 public MainWindow()
 {
     InitializeComponent();
     SourceInitialized += MainWindow_SourceInitialized;
 }

 private void MainWindow_SourceInitialized(object? sender, EventArgs e)
 {
     SetPinning();
 }

 private void SetPinning()
 {
     IntPtr hwnd = new WindowInteropHelper(this).Handle;

     // Define the property key for System.AppUserModel.PreventPinning
     NativeWin32.PROPERTYKEY propKey = new NativeWin32.PROPERTYKEY(new Guid("{9F4C2855-9F79-4B39-A8D0-E1D42DE1D5F3}"), 9);

     // Get the IPropertyStore for the window
     NativeWin32.IPropertyStore propStore;
     int hr = NativeWin32.SHGetPropertyStoreForWindow(hwnd, ref NativeWin32.IID_IPropertyStore, out propStore);
     if (hr != 0) // if failed
     {
         Marshal.ThrowExceptionForHR(hr);
     }

     try
     {
         // Create a PROPVARIANT with bool value: true
         NativeWin32.PROPVARIANT pv = new NativeWin32.PROPVARIANT();
         pv.SetValue(true);

         // Set the property
         propStore.SetValue(ref propKey, ref pv);

         // We must free the PROPVARIANT
         NativeWin32.PropVariantClear(ref pv);
     }
     finally
     {
         // Release the IPropertyStore
         Marshal.ReleaseComObject(propStore);
     }
 }