LS NAV - Non-Inventory Items - Miscellaneous Charges, Services - Create an item that does not track stock

Retail Items>Invoicing>Tick No Stock Posting

Core NAV does not have any options to prevent stock posting.
Items>Inventory Value Zero only affects cost posting, but will still track stock
You need to transact directly against a GL account instead of using an item, or use a Service Item
Or periodically adjust stock to 0.