Inventory Starting Balances

I know it’s not doable by default but maybe there is a workaround. I would like to have the starting balance of an inventory item to show up divided in two parts: opening balance and purchases.

How would you do?

You would not, because the starting balance of an inventory item refers to the physical count of items on hand. See the Notes at the bottom of https://www.manager.io/guides/5497.