When creating a Sales Document for Shopify orders, it is possible to define in Shopify Shipment Method Mapping table (table 30131) that Shipping Charges are handled as an Item, as a G/L Account or as an Item Charge. In a case company operates in different countries, it is important that the Shipping Charges are handled as an Item, because then you can define the correct posting setup for different countries.

That's why I suggest, that the Shipment Method Mapping table would also include the Shipping Charges Type for Credit Memos.