decrypt() returning incorrect result

Oh, thank you for the investigation.
I got your situation.

Try:

PHP Code:

$config        = new Encryption();
$config->driver = 'OpenSSL';
// Your CI3's encryption_key
$config->key            = 'Your Key';
$config->cipher        = 'AES-128-CBC'; // Add this!
$config->rawData        = false;
$config->encryptKeyInfo = 'encryption';
$config->authKeyInfo    = 'authentication';

$encrypter = Services::encrypter($config, false); 


Excellent.  This works. I submitted a PR to add the field into \App\Config\Encryption.php and the documentation example. https://github.com/codeigniter4/CodeIgniter4/pull/7278