Placing Components with Drupal's Extra Fields in drupal 9

nymudule.module

<?php

// In mymodule.module :

use Drupal\node\Entity\NodeType;
use \Drupal\Core\Entity\EntityInterface;
use \Drupal\Core\Entity\Display\EntityViewDisplayInterface;


/**
 * Implements hook_entity_extra_field_info().
 */
function my_module_entity_extra_field_info() {
  $extra = [];

  foreach (NodeType::loadMultiple() as $bundle) {
    $extra['node'][$bundle->Id()]['display']['my_own_pseudo_field'] = [
      'label' => t('My own field'),
      'description' => t('This is my own pseudo-field'),
      'weight' => 100,
      'visible' => TRUE,
    ];
  }

  return $extra;
}


/**
 * Implements hook_ENTITY_TYPE_view().
 */
function my_module_node_view(array &$build, EntityInterface $entity, EntityViewDisplayInterface $display, $view_mode) {
  if ($display->getComponent('my_own_pseudo_field')) {
     $build['my_own_pseudo_field'] = [
        '#type' => 'markup',
        '#markup' => 'This is my custom content', 
     ];
  }
}