get_order_weight_woocommerce.php

<?php
//Save cart weight
add_action( 'woocommerce_checkout_update_order_meta', 'musilda_save_cart_weight' );
function musilda_save_cart_weight( $order_id ) {
    $weight = WC()->cart->get_cart_contents_weight();
    update_post_meta( $order_id, 'order-weight', $weight );
}

//Update all orders
$args = array(
    'status' => array(  'processing', 'completed'),
    'limit' => -1,
);
$orders = wc_get_orders( $args );
if( isset( $orders ) ){
  
    foreach ( $orders as $order ){
        $weight = 0;
        foreach ( $order->get_items() as $key => $item_data ) {
           
          $product = $item_data->get_product();
          $weight += $product->get_weight();

        }   
        update_post_meta( $order->get_id(), 'order-weight', $weight );
    }
}