class EventCreationType extends AbstractType
{
    public function buildForm(FormBuilderInterface $builder, array $options): void
    {
        $builder
            ... adding other fields
            ->add('participants', LiveCollectionType::class, [
                'allow_add' => true,
                'allow_delete' => true,
                'by_reference' => false,
                'entry_type' => EventParticipantType::class, // => only a FormType with 2 fields : name and email text field and both should be not null and not blank
            ])
        ;
    }
...
}

  $component = $this->createLiveComponent(EventForm::class);
  
  $component->submitForm(['event_creation' => [
     ... other fields
      'participants' => [
          [
              'name' => "participant_1",
              'email' => "[email protected]"
          ],
           [
              'email' => "[email protected]",
              'name' => "participant_2"
          ],
      ]
  ]], 'save');

 [
 ... other fields
  "participants" => array:2 [
    0 => array:1 [
      "email" => "[email protected]"
    ]
    1 => array:1 [
      "name" => "participant_2"
    ]
  ]
]

#[AsLiveComponent]
final class EventForm extends AbstractController
{
    use DefaultActionTrait;
    use ComponentWithFormTrait;
    use LiveCollectionTrait;

    #[LiveProp]
    public ?EventCreation $formData = null;

    /**
     * @return FormInterface<EventCreation>
     */
    protected function instantiateForm(): FormInterface
    {
        return $this->createForm(EventCreationType::class, $this->formData ?? new EventCreation());
    }

    #[LiveAction]
    public function save(MessageBusInterface $bus): \Symfony\Component\HttpFoundation\RedirectResponse
    {
        dd($this->formValues);
        
        // Submit the form! If validation fails, an exception is thrown
        // and the component is automatically re-rendered with the errors
        $this->submitForm();

      ... treatment of the information
    }
}