Good to see you here in the Community. I'm here to share some details about QuickBooks Online features in different versions.
QuickBooks Online (QBO) have different versions and features. Currently, the option to create and send purchase orders is not available on the version you're using right now, which is why the Purchasing information box doesn't appear when creating a non-inventory item.
To compare the online versions of QuickBooks, you can check this article: QuickBooks Online.