Inventory cash flows vs COGS difference, therefore, decrease, between, someone

Mechanic

Can someone please clarify the difference between a decrease in inventory on the cash flow statement (cash inflow), vs. cost of goods sold?

COGS = opening stock + purchases - closing stock

But in the above formula, the difference is a change in inventory, which is captured as a change in working capital...isn't' that double counting? Is a decrease in inventory not the same thing as inventory that was converted to sale and therefore COGS?