// Note: products shortcode docs https://docs.woocommerce.com/document/w ... #section-6
// In order for the snippet to work, you must add the parameter orderby = "stock" to the shortcode
// You can add more parameters to it of course e.g. limit, paginate, etc. It's all in the docs
 
add_filter('woocommerce_shortcode_products_query', 'bbloomer_sort_by_stock_status_shortcode', 999, 3);
function bbloomer_sort_by_stock_status_shortcode( $args, $atts, $type ) {
    if ( $atts['orderby'] == "stock" ) {
        $args['orderby']  = array( 'meta_value' => 'ASC' );
        $args['meta_key'] = array('_stock_status';
    }
    return $args;
}