Hello there, rbean.
Good to see you in here QuickBooks Community. I'm here to help and provide some insights about inactive item for Purchase Order (PO) and Invoice.
I've replicated this in my QuickBooks Online (QBO) sample file, when I inactivate an item and create a PO or Invoice it seems like it's not showing when selecting the Product/Service option. Additionally, once you've already created transactions for the inactive item, it will still show on the Sales Transactions window.
However, if you're trying to inactivate an item you can follow this article and scroll down to Delete a list element for the detailed steps: How to edit, delete, and restore list elements.
I also attached the link of our phone support just in case you need further assistance with the steps: Get help with QuickBooks Online.
If you're referring to something else, please don't hesitate to click the Reply button. Any additional details you can share would be appreciated. Have a good one.
