It is not a return: there is no parcel coming back, so there is no return processing cost and no restocking. Treating the two the same overstates your logistics costs and understates your fees, which is why a chargeback and a return are not the same cost.
In a P&L the disputed amount belongs with returns and the fee belongs with transaction costs, attributed to the gateway that charged it. On the nouz statement a Shopify Payments dispute the merchant lost or accepted comes off as a return on the day Shopify closed it, once the store has given nouz permission to read its disputes. The fee is a transaction cost on the day Shopify charged it, where the store lets nouz read its Shopify Payments account; a store without that access has the fee missing from the statement, so it belongs on the month-end checklist: Shopify lists each dispute with its fee, and its Orders page filters by chargeback status.
A handful of chargebacks is a cost of taking cards; a rising rate is a signal about fraud, product claims or delivery times, and it deserves attention long before the fees hurt, because providers price and even terminate accounts on it. The payment fee calculator carries a chargeback line for exactly this reason.