I appreciate you for going through the steps provided in one of our articles, @GCC13.
I’m here to share with you some insights about changing item types in your QuickBooks Desktop (QBDT) software.
Changing an Inventory type item to a Non-inventory item isn’t possible. You only have the option to change it to an Inventory Assembly type item. I’ve attached an image below for your visual reference. 
As a way around, you’ll want to copy the detail of the item and create a new one. Once done, you can either make the item inactive or delete it. For more details about this, you can refer to this article in managing your items: Add, edit, and delete items.
You might also want to check these links for additional reference in tracking your inventories effectively:
I’ll be around in case you have any follow-up questions about inventories in QuickBooks. I’m always around to help you. Keep safe and take care!