Config schema expects keys to be in underscore case

  /**
   * Get default Masonry options.
   *
   * @return array
   *   An associative array of default options for Masonry.
   *   Contains:
   *   - layoutColumnWidth: The width of each column (in pixels, percentage or as
   *     a CSS selector).
   *   - gutterWidth: The spacing between each column (in pixels, percentage or as
   *     a CSS selector).
   *   - isLayoutResizable: Automatically rearrange items when the container is
   *     resized.
   *   - isLayoutAnimated: Animate item rearrangements.
   *   - layoutAnimationDuration: The duration of animations (in milliseconds).
   *   - isLayoutFitsWidth: Sets the width of the container to the nearest
   *     column. Ideal for centering Masonry layouts.
   *   - isLayoutRtlMode: Display items from right-to-left.
   *   - isLayoutImagesLoadedFirst: Load all images first before triggering
   *     Masonry.
   *   - isLayoutImagesLazyLoaded: Custom observer to support layout rebuild in
   *     lazysizes images lazy loading.
   *   - imageLazyloadSelector: lazyLoad class selector used by lazysizes.
   *   - imageLazyloadedSelector: lazyLoaded class selector used by lazysizes.
   *   - stampSelector: Specifies which elements are stamped within the layout
   *     using css selector.
   *   - isItemsWidthForce: Forces the items width to column width.
   *   - isItemsPositionInPercent: Sets item positions in percent values, rather
   *     than pixel values.
   */
  public function getMasonryDefaultOptions() {
    $options = [
      'layoutColumnWidth' => '',
      'gutterWidth' => '0',
      'isLayoutResizable' => TRUE,
      'isLayoutAnimated' => TRUE,
      'layoutAnimationDuration' => 500,
      'isLayoutFitsWidth' => FALSE,
      'isLayoutRtlMode' => ($this->languageManager->getCurrentLanguage()->getDirection() == LanguageInterface::DIRECTION_RTL),
      'isLayoutImagesLoadedFirst' => TRUE,
      'isLayoutImagesLazyLoaded' => FALSE,
      'imageLazyloadSelector' => 'lazyload',
      'imageLazyloadedSelector' => 'lazyloaded',
      'stampSelector' => '',
      'isItemsWidthForce' => TRUE,
      'isItemsPositionInPercent' => FALSE,
      'extraOptions' => [],
    ];

    // Loazyloading classes are auto-calculated for user simplicity. When
    // lazysizes is used without a Drupal module, this means DX is able to use
    // hook_masonry_default_options_alter or hook_masonry_options_form_alter to
    // override this setting.
    if ($this->moduleHandler->moduleExists('lazy')) {
      $config = $this->configFactory->get('lazy.settings');
      $options['imageLazyloadSelector'] = $config->get('lazysizes.lazyClass');
      $options['imageLazyloadedSelector'] = $config->get('lazysizes.loadedClass');
    }

    return $options;
  }