In PHP, what are the best practices for handling form submission that requires processing on the server and displaying results in a new window/tab?

When handling form submission that requires processing on the server and displaying results in a new window/tab, it is best practice to use a combination of PHP and JavaScript. Upon form submission, the PHP script processes the data and generates the results. Then, the PHP script sends the results back to the client-side JavaScript, which opens a new window/tab and displays the results to the user.

<?php
// Process form submission
if ($_SERVER["REQUEST_METHOD"] == "POST") {
    // Process form data here
    
    // Generate results
    $results = "Results of form submission";
    
    // Send results to client-side JavaScript
    echo "<script>
            let newWindow = window.open('', '_blank');
            newWindow.document.write('<h1>Results</h1><p>$results</p>');
          </script>";
}
?>