Hi everyone,

I believe I found a way to do this, even though I couldn't find any way shared online to do so and QB Online support wasn't much help.

It worked for me. Give this a try:

Go to an old (perhaps paid) invoice, a legacy invoice if you will. You may find one or more of these legacy invoices appear to be in the modern format. The modern view has trouble displaying these invoices and this seems to be the key to forcing a reversion. Look to the right of the screen for a button that lets you change the layout or template. It may be buried in a menu, but again it's a long the right side of the screen. (I don't want to go through the process again because I'm afraid of messing with my company's invoicing system just to get the exact procedure.)

That's it, you can select the option to revert to an old template there and it forces a reversion more generally, even if you no longer have the "switch to old layout button. Hope this helps others.