NavigationTestBlockHooks.php

<?php

declare (strict_types=1);
namespace Drupal\navigation_test_block\Hook;

use Drupal\Core\Hook\Attribute\Hook;

/**
 * Hooks implementations for navigation_test_block module.
 */
class NavigationTestBlockHooks {
  
  /**
   * Implements hook_block_alter().
   */
  public function blockAlter(&$definitions) : void {
    $definitions['navigation_test']['allow_in_navigation'] = TRUE;
  }
  
  /**
   * Implements hook_navigation_defaults().
   */
  public function navigationDefaults() : array {
    $blocks = [];
    $blocks[] = [
      'delta' => 1,
      'configuration' => [
        'id' => 'navigation_test',
        'label' => 'My test block',
        'label_display' => 'visible',
        'provider' => 'navigation_test_block',
      ],
    ];
    return $blocks;
  }

}