Quickbooks Desktop doesn't behave with emailed invoice templates.
It's nice to see you here in the Community, @robclay.
Thanks for sharing the steps you've tried and providing a screenshot. I can help remove that section, so your customer will only see the template that you created when sending an invoice in QuickBooks Desktop (QBDT).
All you need to do is to enable the Use Plain Text format for e-mailed invoices on the Preferences. Here's how:
1. Go back to Edit menu at the top, then choose Preferences on the drop-down. 2. Pick Send Forms again on the left panel, and go to My Preferences tab. 3. Put a checkmark on the Use Plain Text format for e-mailed invoices, then click OK.
That should do the trick! You may create a dummy invoice and send it to your personal email to double-check.