How to check the item ‘maintain_stock’ value from sales invoice via custom script?
Do you want the number of items in stock, or just whether the Maintain Stock is checked or not in the item master? Do you want the value to appear on the printed invoice or only on the Sales Invoice form, in the Sales Invoice Item table? It may be possible to add a field in the Sales Invoice Item table that is linked to the is_stock_item in the Item form/doctype.
Maybe create a button that do “Check Maintain Stock” via custom script?