Cacher is the code snippet organizer for pro developers

// Display featured products in shop pages
add_filter( 'woocommerce_product_query_tax_query', 'custom_product_query_tax_query', 10, 2 );
function custom_product_query_tax_query( $tax_query, $query ) {
    if( is_admin() ) return $tax_query;

    if ( is_shop() ) {
        $tax_query[] = array(
            'taxonomy' => 'product_visibility',
            'field'    => 'name',
            'terms'    => 'featured'
        );
    }

    return $tax_query;
}