I am well aware of how significant the add subtotal button is in your business, @wheyland electric. No worries. I'm here to walk you through the steps for adding the subtotal button in the new invoice layout in QuickBooks Online (QBO).

The Add a Subtotal button is already included in the new and updated invoice layout.

Here's how:

1. Go to the +New icon.
2. Select Invoice.
3. On the invoice page, scroll down below the Product or Service.
4. Click the Add product or service drop-down.
5. Choose the Add a subtotal.
6. Fill out the necessary fields.
7. Once done, hit Save or Review and send.

Furthermore, you might want to check this article I've included and learn how to personalize and add specific info to your sales forms: Customize invoices, estimates, and sales receipts in QuickBooks Online.

I'm always available to assist if you require additional assistance managing your invoices. Just leave a reply in the comments. Have a good day ahead!