How to change the label of an image's title field in a paragraph

I finally achieved what I wanted doing the following

mymodule/mymodule.module

use Drupal\Core\Form\FormStateInterface;
use Drupal\mymodule\Alter\FieldWidget\BlockImagesParagraph;

/**
 * Implements hook_field_widget_single_element_WIDGET_TYPE_form_alter().
 */
function mymodule_field_widget_single_element_entity_reference_paragraphs_form_alter(&$element, FormStateInterface $form_state, $context) {
  if ($element['#paragraph_type'] == 'block_images') {
    \Drupal::service('class_resolver')
      ->getInstanceFromDefinition(BlockImagesParagraph::class)
      ->alterFieldWidget($element, $form_state, $context);
  }
}

mymodule/src/Alter/FieldWidget

namespace Drupal\mymodule\Alter\FieldWidget;

use Drupal\Core\Form\FormStateInterface;

/**
 * Alter block_images paragraph.
 */
final class BlockImagesParagraph {

  /**
   * Alter the field widget.
   *
   * @param array $element
   *   The field widget form element.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   * @param array $context
   *   An associative array representing the context.
   */
  public function alterFieldWidget(array &$element, FormStateInterface $form_state, array $context) {
    $widget = &$element['subform']['image']['widget'];

    foreach ($widget as $key => &$value) {
      if (!is_int($key)) {
        continue;
      }
      $value['#process'][] = [
        'Drupal\mymodule\Alter\FieldWidget\BlockImagesParagraph',
        'processImageWidget',
      ];
    }
  }

  /**
   * Process the image widget.
   *
   * @param array $element
   *   The field widget form element.
   * @param \Drupal\Core\Form\FormStateInterface $form_state
   *   The form state.
   * @param array $form
   *   An associative array representing the form.
   */
  public static function processImageWidget(array $element, FormStateInterface $form_state, array $form) {
    if (isset($element['title'])) {
      $element['title']['#title'] = t('Caption');
    }

    return $element;
  }

}