A PHP script of how to directly output Xlsx (Excel) file when a user access a webpage

excel_web.php

<?php
require_once 'vendor/autoload.php';

use PhpOffice\PhpSpreadsheet\Spreadsheet;
use PhpOffice\PhpSpreadsheet\Writer\Xlsx;

$spreadsheet = new Spreadsheet();
$sheet = $spreadsheet->getActiveSheet();
$sheet->setCellValue('A1', 'Hello World !');
$writer = new Xlsx($spreadsheet);

$filename = 'hello world';

header('Content-Type: application/vnd.openxmlformats-officedocument.spreadsheetml.sheet');
header('Content-Disposition: attachment;filename="' . $filename . '.xlsx"');
header('Cache-Control: max-age=0');

$writer->save('php://output');

php://output is a writable stream that is sent to Apache and will be returned to the browser that requested your page.
Cr. https://stackoverflow.com/a/7186297/7150241