It's nice to have you here in the Community, @vevans.
I'll provide information about the Copy to a Purchase Order command in QuickBooks Online (QBO).
Currently, the option to Copy to a Purchase Order directly through the estimate or invoice interface is unavailable. However, you can still copy the estimate in the Sales section. To do so, follow the steps below:
- Go to the left navigation panel and select Sales.
- In the Sales section, choose Estimates.
- Locate the estimate that you want to Copy to purchase order.
- Click the drop-down button of that estimate and select copy to purchase order.
You can also refer to the screenshot provided below for visual guidance:

I'll also add these articles that'll help you organize your accounts, customers, and vendors, as well as help you designate a preferred vendor for specific inventory items to streamline the ordering process and save time:
In case you have any follow-up questions regarding the copy to a purchase order or anything else related to QuickBooks, feel free to ask me. I'm always here to help you, @vevans. Take care!