I have a function like this

function data_process(){
    var output = HtmlService.createHtmlOutput('<b>Processing the Data!!</b>')
                          .setHeight(150)
                          .setWidth(200);
    SpreadsheetApp.getUi().showModalDialog(output, '⚙️ Processing..');
    Utilities.sleep(1000);  

    /* Here I am Building an chart into new sheet. There is no issue in chart creation 
 and creating an new sheet for charts */

  var output = HtmlService.createHtmlOutput('<script>google.script.host.close();/script>');
  SpreadsheetApp.getUi().showModalDialog(output, 'Loading...');
}

I am referring to this solutions
[1]: Auto close modal dialog – After server code is done, close dialog in Google Spreadsheet

Modal box does not shows up and no error as well. Any help is much appreciated. Thanks in advance.