Layout builder notes.md

Remove default layouts

/**
 * Implements hook_plugin_filter_TYPE__CONSUMER_alter()
 */
function custom_layouts_plugin_filter_layout__layout_builder_alter(&$definitions) {

  // Remove layouts that are NOT provided by this module.
  foreach ($definitions as $id => &$definition) {
    if ($definition->getProvider() != 'custom_layouts') {
      unset($definitions[$id]);
    }
  }
}