In the API 2026-04 release candidate version, a new field, remainingLineItemsWeight, has been added to the FulfillmentOrder GraphQL type. This field returns the total weight of line items that haven’t been fulfilled yet, which enables you to make decisions based on remaining weight in your fulfillment order.
This is a companion discussion topic for the original entry at https://shopify.dev/changelog/remaining-line-items-weight-available-for-fulfillment-orders