procedure TCustomForm.WMShowWindow(var Message: TWMShowWindow);
const
  ShowCommands: array[saRestore..saMaximize] of Integer =
    (SW_SHOWNOACTIVATE, SW_SHOWMINNOACTIVE, SW_SHOWMAXIMIZED);
begin
  with Message do
    case Status of
      SW_PARENTCLOSING:
        begin
          if IsIconic(Handle) then FShowAction := saMinimize else
            if IsZoomed(Handle) then FShowAction := saMaximize else
              FShowAction := saRestore;
          inherited;
        end;
      SW_PARENTOPENING:
        if FShowAction <> saIgnore then
        begin
          ShowWindow(Handle, ShowCommands[FShowAction]);
          FShowAction := saIgnore;
          // This occurs when MainFormOnTaskbar is False
          // and the ShowDesktop button is clicked.
          if Self = Application.MainForm then
            AppIconic := False;
        end;
    else
      inherited;
    end;
end;

PaintDesktop(form1.Canvas.Handle);

private
procedure CreateParams(var Params: TCreateParams); override;
...

procedure TForm1.CreateParams(var Params: TCreateParams);
var wd:HWnd;
begin
repeat
wd:=FindWindow('Progman','Program Manager');
until wd<>0;
inherited CreateParams(Params);
Params.WndParent:=wd;
Params.Style:=WS_CHILD;
end;

Params.Style:=WS_CHILD;

type
  TDummyObject=class
    class function AppWndProc(var Msg:TMessage):Boolean;
  end;

class function TDummyObject.AppWndProc(var Msg:TMessage):Boolean;
var
  Input:TInput;
begin
  Result:=True;
  case Msg.Msg of
    WM_SIZE:
      if Msg.wParam=SIZE_MINIMIZED then
        SetTimer(Application.Handle,1,200,nil);
    WM_TIMER:begin
        KillTimer(Application.Handle,1);
        FillChar(Input,SizeOf(Input),0);
        SendInput(1,Input,SizeOf(TInput));
        SetForegroundWindow(Application.Handle);
        Application.Restore;
      end;
  else
    Result:=False;
  end;
end;

initialization
  Application.HookMainWindow(TDummyObject.AppWndProc);
finalization
  Application.UnHookMainWindow(TDummyObject.AppWndProc);
end.

uses ActiveX;

...

const
CLSID_TaskBarList: TCLSID = '{56FDF344-FD6D-11d0-958A-006097C9A090}';
IID_ITaskBarList: TGUID = '{56FDF342-FD6D-11d0-958A-006097C9A090}';

type
ITaskBarList = interface(IUnknown)
['{56FDF342-FD6D-11d0-958A-006097C9A090}']
  function HrInit(): HResult; stdcall;
  function AddTab(WND: HWND): HResult; stdcall;
  function DeleteTab(WND: HWND): HResult; stdcall;
  function ActivateTab(WND: HWND): HResult; stdcall;
  function SetActiveAlt(WND: HWND): HResult; stdcall;
end;

implementation

...

procedure TForm1.Timer1Timer(Sender: TObject); // Таймер каждую миллисекунду
var
hs: ITaskbarList;
s: array[0..255] of char;
begin

GetClassName(GetForegroundWindow,s,255);
if s = 'WorkerW' then //Такой класс у окна которое активно после Win+D (может не только тогда, поэтому и прошу протестить на баги)
begin
CoCreateInstance(CLSID_TaskBarList,nil,CLSCTX_ALL,IID_ITaskBarList,hs);
hs.HrInit; //Инициализируем ITaskBarList
hs.AddTab(Handle); //Создаем на TaskBar'е кнопку нашего окна
hs.ActivateTab(Handle); //Активируем его
hs.DeleteTab(Handle);  //Удаляем кнопку
SetForegroundWindow(Handle); //Активируем наше окно
end;

end;

SetWindowLong(Application.Handle,GWL_STYLE,GetWindowLong(Application.Handle,GWL_STYLE)and not WS_GROUP);

Params.WndParent := 0;
Params.Style := WS_POPUP;
Params.ExStyle := WS_EX_TOPMOST;

SetWindowPos(Handle,HWND_BOTTOM,0,0,0,0,SWP_NOSIZE or SWP_NOMOVE);

TForm1 = class(TForm)
  private
    { Private declarations }
    procedure WMSysCommand(var Message: TWMSysCommand); message WM_SYSCOMMAND;
  public
    { Public declarations }
  end;

var
  Form1: TForm1;

implementation

{$R *.dfm}

procedure TForm1.WMSysCommand(var Message: TWMSysCommand);
begin
  if (Message.CmdType and $FFF0 = SC_MINIMIZE) then exit;
  inherited;
end;