New improved version

This new version is more performant, automatically ignore some fields that are default in wordpress and fix the issue of the blank page.

<?php
/*
Plugin Name: Export Users to CSV
description: Export Users to CSV Plugin allows you to export users list and their metadata in CSV file.
Version: 1.4
Author: Boopathi Rajan
Author URI: https://www.boopathirajan.com
License: GPLv2 or later
License URI: https://www.gnu.org/licenses/gpl-2.0.html
*/

function eu_register_export_page() {
    add_submenu_page('tools.php', 'Export Users', 'Export Users', 'manage_options', 'wp-export-users', 'eu_export_users_page');
}
add_action('admin_menu', 'eu_register_export_page');

function eu_export_users_page() {
}

add_action('admin_init', 'eu_export');

function eu_export() {
    if (!isset($_GET['page']) || isset($_GET['page']) && $_GET['page'] !== 'wp-export-users') {
        return;
    }
    global $wpdb, $table_prefix;
    ob_end_clean();
    header('Content-Type: application/csv');
    header('Content-Disposition: attachment; filename="' . time() . '.csv";');
    $file = fopen('php://output', 'w');
    $ignore_sql = ' WHERE ';
    foreach (array(
        'meta-box',
        'metabox',
        'closedpostboxes',
        'dashboard',
        'nag',
        'managenav',
        'password',
        'ssl',
        'dismissed',
        'admin',
        'token',
        'jetpack',
        'menu',
        'elementor',
        'wpcom',
        'submit',
        'syntax',
        'panel',
        'shortcut',
        'editing',
        $table_prefix
    ) as $ignore_me) {
        $ignore_sql .= "meta_key NOT LIKE '%" . $ignore_me . "%' AND ";
    }
    $meta_sql = 'SELECT meta_key FROM ' . $wpdb->usermeta . $ignore_sql . " meta_key!='first_name' AND meta_key!='last_name' GROUP BY meta_key";
    $users = get_users( array( 'orderby' => 'ID','order' => 'ASC' ) );
    $meta_keys = $wpdb->get_results($meta_sql);
    $datas = array();
    $headers = array(
        'ID',
        'Username',
        'Email',
        'Display Name',
        'First Name',
        'Last Name',
        'Registered Date'
    );
    if ($users) {
        foreach ($users as $user) {
            $user_meta = get_userdata($user->ID);
            $user_data = array();
            $user_data[] = $user->ID;
            $user_data[] = $user->user_login;
            $user_data[] = $user->user_email;
            $user_data[] = $user->display_name;
            $user_data[] = $user_meta->first_name;
            $user_data[] = $user_meta->last_name;
            $user_data[] = $user->user_registered;
            if (!empty($meta_keys)) {
                foreach ($meta_keys as $meta_key) {
                    $key = $meta_key->meta_key;
                    if (!isset($headers[$key])) {
                        $headers[$key] = $key;
                    }
                    if (is_object($user_meta->$key) || is_array($user_meta->$key)) {
                        if (is_array($user_meta->$key) && count($user_meta->$key) == 1 && isset($user_meta->$key[0])) {
                            $user_data[] = $user_meta->$key[0];
                        }
                        else {
                            $user_data[] = serialize($user_meta->$key);
                        }
                    }
                    else {
                        $user_data[] = $user_meta->$key;
                    }
                }
            }
            $datas[] = $user_data;
        }
    }

    fputcsv($file, $headers);
    foreach ($datas as $data) {
        fputcsv($file, $data);
    }
    fclose($file);
    exit();
}

/* Add action links to plugin list*/
add_filter('plugin_action_links_' . plugin_basename(__FILE__) , 'eu_add_export_user_action_links');
function eu_add_export_user_action_links($links) {
    $settings_link = array(
        '<a href="' . admin_url('tools.php?page=wp-export-users') . '">Export Users</a>'
    );
    return array_merge($links, $settings_link);
}