From the GP team:
“… information and troubleshooting tips around the On Order amount on the Item Quantities Maintenance window. If you go to Inventory >> Cards >> Quantities…”
On Order field in the Item Quantities Maintenance window shows a quantity, but there are no Purchase Orders listed when zooming to view the details – Microsoft Dynamics GP Community
Archived post from 2020. Dynamics GP and the links it points to have changed since; check current documentation before relying on version-specific steps.