Warum werden die Daten trotz Session_destroy() immer noch vom Browser erkannt?

The issue may be due to the fact that the session cookie is still stored in the browser even after calling session_destroy(). To completely remove the session cookie from the browser, you can also unset the session cookie by setting its expiration time to a past date. This will force the browser to remove the session cookie.

// Start the session
session_start();

// Unset all session variables
$_SESSION = array();

// Destroy the session
session_destroy();

// Unset the session cookie
if (ini_get("session.use_cookies")) {
    $params = session_get_cookie_params();
    setcookie(session_name(), '', time() - 42000, $params["path"], $params["domain"], $params["secure"], $params["httponly"]);
}