trouble to create a contactform with CakePHP 4 - cakephp

Question

I started using cakePHP 4 a while ago and my website is quite done. But i have some trouble creating a contact Form. I did as instructed on the cookbook > Modelless Forms, Validation and Forms but i do not get it right (for me the cookbook is really hard to understand sometimes).
When i press my button to send the form, the same page appears with filled fields but no validation or error messages are shown. I am sure i forgot something to send these information from the controller and something to get these data from the controller but ... i cant find what exactly i need. Also i do not exactly understand what i have to fill in the ContactController "$this->request->is('get')"i hope someone of you can help me out of there. Maybe i just have a big board in front of my head...
here is my code (the templatecode is just a excerpt)
src/Controller/ContactController.php
<?php
namespace App\Controller;
use App\Controller\AppController;
use App\Form\ContactForm;
class ContactController extends AppController
{
public function index()
{
$contact = new ContactForm();
if ($this->request->is('post')) {
if ($contact->execute($this->request->getData())) {
$this->Flash->success('We will get back to you soon.');
} else {
$this->Flash->error('There was a problem submitting your form.');
$contact->setErrors(['name' => ['_required' => 'at least 5 signs'],['email' => ['_required' => 'Your email is required']]);
}
}
if ($this->request->is('get')) {
$contact->setData([
'name' => 'John Doe',
'email' => 'john.doe#example.com'
]);
}
$this->set('contact', $contact);
}
}
src/Form/ContactForm.php
<?php
/* https://book.cakephp.org/4/en/core-libraries/form.html */
namespace App\Form;
use Cake\Form\Form;
use Cake\Form\Schema;
use Cake\Validation\Validator;
class ContactForm extends Form
{
protected function _buildSchema(Schema $schema): Schema
{
return $schema->addField('name', 'string')
->addField('email', ['type' => 'string'])
->addField('subject', ['type' => 'string'])
->addField('message', ['type' => 'text']);
}
public function validationDefault(Validator $validator): Validator
{
$validator->minLength('name', 5)
->email('email')
->notEmptyString('subject', 'Please fill this field')
->notEmptyString('text', 'Please fill this field')
return $validator;
}
protected function _execute(array $data): bool
{
print_r('TESTING OK');
return true;
}
public function setErrors($errors)
{
$this->_errors = $errors;
}
}
templates/Pages/contact.php (used with ready HTML Templates for the style)
...
<?php echo $this->Form->create($contact); ?>
<div class="row gtr-50 gtr-uniform">
<div class="col-6 col-12-mobilep">
<?php echo $this->Form->control('name',['label' => false,'placeholder'=>$translation['Name'],'templates' => ['inputContainer' => '{{content}}']]);?>
</div>
<div class="col-6 col-12-mobilep">
<?php echo $this->Form->control('email',['label' => false,'placeholder'=>$translation['Email'],'templates' => ['inputContainer' => '{{content}}']]);?>
</div>
<div class="col-12">
<?php echo $this->Form->control('subject',['label' => false,'placeholder'=>$translation['Betreff'],'templates' => ['inputContainer' => '{{content}}']]);?>
</div>
<div class="col-12">
<?php echo $this->Form->textarea('message',['label' => false,'placeholder'=>$translation['Bitte gebe deine Nachricht ein'],'rows'=>'6']); ?>
</div>
<div class="col-12">
<ul class="actions special">
<li><?php echo $this->Form->submit($translation['Nachricht senden']); ?></li>
</ul>
</div>
</div>
<?php echo $this->Form->end(); ?>
...
Thanks a lot