Hello there, @Mark E W.
The option to make the number of copies as default is unavailable in QuickBooks Desktop Premier version 2019. Although, you can check your actual printer's settings to make default copies to one.
Please take note that some of the printer's settings don't have this default option such as the Fuji Xerox Laser printer. For now, you'll have to enter one copy every time you print your invoice.
I added an article to know the updates of QuickBooks Desktop versions: Working with QuickBooks Desktop Pro, Premier, and Enterprise. You can scroll down to see the topic, "What's New in QuickBooks Desktop".
I'll be here if you have other concerns or questions for QuickBooks. Stay safe and have a wonderful day ahead.
