security – Is my website’s PHP registration system secure?

I would like to know if my registration system is secure. I’m not sure if it is secure, as I’m new in development, and I’m afraid that the system is flawed

Also, I’m not experienced in object oriented programming, I would like to know if my script looks a bit like OOP or is simply a set of procedural programming with object oriented

database.php

<?php

/**
 * Class responsible for connecting to the database
 * It will be inherited by the SignUp class
 */
class DatabaseConnection
{
    public function __construct(string $host, string $dbname, string $username, string $password)
    {
        try{
            $this->database = new PDO("mysql:host=$host;dbname=$dbname;charset=utf8mb4", $username, $password);
        }catch(PDOException $e){
            throw new Exception($e->getMessage());
        }
    }
}

registration.php

<?php

/**
 * This is a registration script
 * @author Anne Batch
 * @copyright 2021
 */

declare(strict_types = 1);

class SignUp extends DatabaseConnection
{
    /**
     * Database Connection
     * @var PDO
     */
    private $database;

    /**
     * @var string
     */
    private $name;

    /**
     * @var string
     */
    private $email;

    /**
     * @var string
     */
    private $passwordHash;

    /**
     * @var string
     */
    private $signUpPage;
    
    /**
     * @param string $name Assign the username
     */
    public function setName(string $name)
    {
        $this->name = $name;
    }

    /**
     * @param string $email Assign the email
     */
    public function setEmail(string $email)
    {
        $this->email = $email;
    }

    /**
     * @param string $password & $confirm Assign password and password confirmation
     */
    public function setPassword(string $password, string $confirm)
    {
        if ($password === $confirm) {
            $options = (
                'cost' => 12,
            );
            $this->passwordHash = password_hash($password, PASSWORD_BCRYPT, $options);
        }
        else {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Passwords does not match!</div>');
        }
    }

    /**
     * @param $signUpPage Redirect Page
     */
    public function signUpPage(string $signUpPage)
    {
        $this->signUpPage = $signUpPage;
    }

    /**
     * @param $errorMessage Notification Message
     */
    private function returnWithError(string $errorMessage)
    {
        $_SESSION('error') = $errorMessage;
        header('Location: ' . $this->signUpPage);
        exit();
    }

    /**
     * Checks whether a name exists
     */
    public function existingName(): void
    {
        $statement = $this->database->prepare("SELECT 1 FROM users WHERE username = :username");
        $statement->execute((
            ":username" => $this->name
        ));
        $exists = $statement->fetchColumn();

        if(!$exists) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Name already exists!</div>');
        }
    }

    /**
     * Checks whether an email exists
     */
    public function existingEmail(): void
    {
        $statement = $this->database->prepare("SELECT email FROM users WHERE email = :email");
        $statement->execute((
            ":email" => $this->email
        ));

        $result = $statement->rowCount();

        if($result != 0) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Email already exists!</div>');
        }
    }

    /**
     * Checks if the fields have been filled
     */
    public function isDefinedFields(): void
    {
        if(!$this->name || !$this->email) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Please, fill out all the fields!</div>');
        }
    }

    /**
     * Checks if the username is less than 3 or greater than 50
     */
    public function ValidateNameLength(): void
    {
        if(mb_strlen($this->name) < 3) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Can only use 3 or more characters as name!</div>');
        }

        if(mb_strlen($this->name) > 50) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Can only use a maximum of 50 characters as name!</div>');
        }
    }

    /**
     * Checks if the email is semantically correct
     */
    public function ValidateEmail(): void
    {
        if(!filter_input(INPUT_POST, $this->email, FILTER_VALIDATE_EMAIL)) {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Incorrect email!</div>');
        }
    }
    
    /**
     * Checks if the username matches the regular expression
     * The purpose of regular expression is to prevent JavaScript attacks
     * The user will not be able to use certain characters, such as <> /
     */
    public function addUser(): void
    {
        if(preg_match("/^(w&.-)*$/", $this->name)) {
                $statement = $this->database->prepare("INSERT INTO users VALUES(?, ?, ?, ?, ?, ?, ?)");
                $statement->execute((
                    $this->name,
                    $this->email,
                    $this->passwordHash,
                    $_SERVER('REMOTE_ADDR'),
                    $_SERVER('HTTP_CLIENT_IP'),
                    $_SERVER('HTTP_X_FORWARDED_FOR'),
                    $_SERVER('HTTP_USER_AGENT')
                ));
                if($statement) {
                    $this->returnWithError('<div class="alert alert-success" role="alert">Registered successfully!<br>Login now</div>');
                }
            }  
        else {
            $this->returnWithError('<div class="alert alert-danger" role="alert">Can only use letters and numbers as name!</div>');
        }
    }
}

main.php

<?php

session_start();

require_once('database.php');
require_once('registration.php');

$users = new SignUp('localhost', 'database', 'root', 'password');
$users->setName($_POST('username'));
$users->setEmail($_POST('email'));
$users->signUpPage('signup');
$users->setPassword($_POST('password'), $_POST('password2'));
$users->existingName();
$users->existingEmail();
$users->isDefinedFields();
$users->ValidateNameLength();
$users->ValidateEmail();
$users->addUser();