private
    { Private-Deklarationen }
    Loader : ITask;


procedure TForm1.ButtonThreadPoolClick(Sender: TObject);
var
  Liste : TStringList;
  Index : Integer;
  Threads : Word;
begin
  Threads := 3;
  if Threads < TThread.ProcessorCount then Threads := TThread.ProcessorCount; //....DAS MÖCHTE ICH NICHT HABEN ....

  TThreadPool.Default.SetMaxWorkerThreads(Threads);
  Label2.Caption := IntToStr(TThreadPool.Default.MaxWorkerThreads); {Nur zur Prüfung}

  Liste := TStringList.Create;
    for Index := 1 to 300 do
      Liste.Add(Index.ToString);

  Loader := TTask.Run(
    procedure
      begin
        TParallel.For(0, Liste.count - 1,
          procedure(I : Integer; ALoopStatus : TParallel.TLoopState) {I wird an die Methode übergeben, damit habe ich den Wert aus der Liste im Thread}
            var
              URL : string;
            begin
              if Loader.Status = TTaskStatus.Canceled then ALoopStatus.Break; {Um Abbruch zu realisieren}

              URL := Liste[I];
              // ...
              Sleep(Random(1000)); {Muster für mach etwas}
              //...

              TTHread.Queue(nil,
                procedure
                  begin
                     with ListView1.Items.Add do
                       begin
                         Caption := URL;
                       end;
                  end);
            end);
        Label1.Caption := 'Fertig';
        FreeAndNil(Liste);
      end);
end;

procedure TForm1.ButtonAbbruchClick(Sender: TObject);
begin
  Loader.Cancel;
end;

  
  Threads := 3;
  TThreadPool.Default.SetMaxWorkerThreads(Threads);