Hello @mckeever-fab-gma,
You have another option to select your custom template as your default form used for a sales receipt. Let me show you how.
To start with, changing the template within the sales receipt can be done under Customize then, putting a checkmark on your created custom template.
But if you don't have the option to do so, follow the steps below to choose your default template:
On top of that, I've also included this reference for a compilation of articles you can read while working with us: Sales and Customer for QuickBooks Online.
If there's anything else that I can help you with, please let me know in the comments below. I'll be here to lend a hand.