Hello, piehtool.

I'd like to help you figure out why you don't have the option to create an invoice on your Sales order fulfillment worksheet. 

The invoice should be shown when you have open Sales orders. Since it's not there, I can guide you on how to troubleshoot the QuickBooks Desktop program. This odd behavior happens when there's an update, system maintenance, or data damage.
 

Let's begin by creating a backup of your company file before updating the program. This is done so that you can undo the changes if there's an error. After updating, you can check back if the data is there.

If there are still no changes, you can proceed to run Verify to scan any program errors. Then, if there's an error you fix it using the Rebuild process. You can refer the steps here: Verify and Rebuild Data in QuickBooks Desktop.

However, if there's no error and the data is still not in the Sales Order Fulfillment Worksheet window, I'd suggest downloading the QuickBooks File Doctor. Here's an article for more information about the steps: QuickBooks Desktop doesn't start or won't open. 

I've added this article for your future tasks about personalizing your forms in QuickBooks Desktop: Use and customize form templates. 

If you need further assistance, I'll be here and ready to help anytime. Have a good day.