graphql.php

<?php 

add_filter( 'graphql_PostObjectsConnectionOrderbyEnum_values', function( $values ) {

  $values['FEATURED'] = [
    'value' => 'featured',
    'description' => __( 'Get only featured items', 'wp-graphql' ),
  ];
  return $values;

} );

add_filter( 'graphql_post_object_connection_query_args', function( $query_args, $source, $input ) {

  if ( isset( $input['where']['orderby'] ) && is_array( $input['where']['orderby'] ) ) {
    foreach( $input['where']['orderby'] as $orderby ) {
      if ( ! isset( $orderby['field'] ) || 'featured' !== $orderby['field'] ) {
        continue;
      }
      $query_args['meta_key'] = 'featured';
      $query_args['meta_value'] = true;
    }
  }
  return $query_args;
}, 10, 3);