Woocommerce shop add ” Default Product Sorting ” drop down option.

function woocommerce_shop_ordering_add_option( $sort_args ){
  	$orderby_value = isset( $_GET['orderby'] ) ? woocommerce_clean( $_GET['orderby'] ) : apply_filters( 'woocommerce_default_catalog_orderby', get_option( 'woocommerce_default_catalog_orderby' ) );
  
    if ( 'alphabetical' == $orderby_value ) {
        $sort_args['meta_key'] = 'property_priority'; 
        $sort_args['orderby'] = 'meta_value';
        $sort_args['order'] = 'DESC';
    }
    return $sort_args;
}
add_filter( 'woocommerce_get_catalog_ordering_args', 'woocommerce_shop_ordering_add_option' );
function woocommerce_catalog_orderby_add_option( $sortby ) {
    $sortby['alphabetical'] = 'Sort by STC';
    return $sortby;
}
add_filter( 'woocommerce_default_catalog_orderby_options', 'woocommerce_catalog_orderby_add_option' );
add_filter( 'woocommerce_catalog_orderby', 'woocommerce_catalog_orderby_add_option' );