You've come to the right place, @daniel67. I have all the steps you need in removing the category details on your purchase order and invoice forms.
You have the option to customize your forms from the Custom form styles page. Follow the instructions below:
- Go to the Gear icon.
- Select Custom form styles.
- Find your template.
- From the Action column, select Edit.
- Under the Content tab, select the second section by clicking the Pencil icon.
- Uncheck the Category box under the Product/Service section.

- Select Done.
You can also set a specific template as default. This way, you won't need to select which template to use every time you send or print forms.

Additionally, to give you more ideas on how to create attractive and professional-looking sales forms, check out this article: Customize invoices, estimates, and sales receipts in QuickBooks Online.
I'm always around if you need further assistance. Have a great day, daniel67.