Can Opening Balances Be Entered in Inventory?

Yes, since inventory contains multiple items, the system allows you to enter opening balances through Managing Requisition.

Go to the Inventory menu, choose Managing Requisition, then Add Manually, then specify the quantity and unit cost for each product.
Select the Opening Balances sub-account, and the system will automatically create the following journal entry:
From: Inventory Account
To: Opening Balances Account