Custom block plugin does not show in Layout Builder options

Newish to Layout Builder - we made a custom block plugin that renders a custom form. When I go to a page with Layout Builder and try to add that block... it is not in the list of blocks.

/**
 * Provides a form block.
 *
 * @Block(
 *   id = "my_block",
 *   admin_label = @Translation("My Block with Form"),
 *   category = @Translation("Custom")
 * )
 */
class MyBlock extends BlockBase implements ContainerFactoryPluginInterface {

  /**
   * The form builder.
   *
   * @var \Drupal\Core\Form\FormBuilderInterface
   */
  protected $formBuilder;

  /**
   * Constructs a new MyBlock instance.
   *
   * @param array $configuration
   *   The plugin configuration, i.e. an array with configuration values keyed
   *   by configuration option name. The special key 'context' may be used to
   *   initialize the defined contexts by setting it to an array of context
   *   values keyed by context names.
   * @param string $plugin_id
   *   The plugin_id for the plugin instance.
   * @param mixed $plugin_definition
   *   The plugin implementation definition.
   * @param \Drupal\Core\Form\FormBuilderInterface $form_builder
   *   The form builder.
   */
  public function __construct(array $configuration, $plugin_id, $plugin_definition, FormBuilderInterface $form_builder) {
    parent::__construct($configuration, $plugin_id, $plugin_definition);
    $this->formBuilder = $form_builder;
  }

  /**
   * {@inheritdoc}
   */
  public static function create(ContainerInterface $container, array $configuration, $plugin_id, $plugin_definition) {
    return new static(
      $configuration,
      $plugin_id,
      $plugin_definition,
      $container->get('form_builder')
    );
  }

  /**
   * {@inheritdoc}
   */
  public function build() {
    $build['access_form'] = $this->formBuilder->getForm('Drupal\mymodule\Form\MyForm');
    return $build;
  }

}

Is there something I need to add to the annotation or class to make it an option for Layout Builder? It works fine as a normal Drupal block.

edit: I notice in one random custom module, they have to alter Layout Builder to get this functionality. Is that correct??

https://git.drupalcode.org/project/layout_builder_block/-/blob/1.x/src/EventSubscriber/LayoutBuilderBlockAddControllerSubscriber.php