You can use the formulas below in the Calculated Fields to export the total shipping refund amount and refund tax amount from an order:

Refund Amount

get_total([oa.amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"])

Refund Tax Amount

get_total([oa.tax_amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"])

Refund Amount + Tax

get_total([oa.amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"]) + get_total([oa.tax_amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"])

This will parse the refunds > order_adjustments subfield and filter the values to only include those where the "kind" is "shipping_refund".

The value will be a negative number.  To make it a positive number, we can simply multiply by -1 like this:

(get_total([oa.amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"]) + get_total([oa.tax_amount for oa in load_json_data(flatten_list([i.order_adjustments for i in load_json_data({{ refunds }})])) if oa.kind == "shipping_refund"])) * -1