Hi there, @Thomjc.
Currently, the option to remove the Tag field in the sales forms is unavailable even when you turn off the feature or delete the tag names. This field will not show on the forms when printed or emailed to your customers.
I've added this article for your future reference in case you want to customize your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.
Please don't hesitate to tag my name in the comment section if you have other questions. I'd be happy to assist you further. Take care.