Seems no answer about this...

what you describe is very clear藍,I also found that what about return order information can get is only event msg,detail about item or return reason is no way,I lost day and day to find a solution but has no result1、Order API：get nothing about return2...

Seems has no API can get this infor,include Stand API and GraphQL API。。。。藍

https://community.shopify.com/c/shopify-apis-and-sdks/return-api/m-p/640771  I only find this article about return order when return status=Return in progress,but i cannot get which item is in return?

which API I can get these info? 

yeah, not find any information about return line items when order  return_status=in_progress 

What I found is Shopify just set return tag on order,when customer return itemreturn_status=in_progress means customer have a return and us have been start process it