Thanks for joining the thread, @JGargiulo.

Currently, the option to have a default attachment for your IRS W-9 form when creating an invoice isn't yet available in QuickBooks Online (QBO). Rest assured, our product engineers are still working on it so this  feature could be added soon. 

Meanwhile, you may consider following the steps suggested by my peer Catherine_B about copying a similar invoice or creating unscheduled recurring transactions. I'd also recommend visiting our QuickBooks Blog to get updated about the latest news and product enhancements. Please use this direct link to access it:https://quickbooks.intuit.com/blog/.

Also, you'll want to learn how to customize your invoices in QBO. This way, you're able to personalize them suited to your business needs and becomes more appealing to your customers. Please refer to this great resource for the steps on how to do the trick: How to customize my invoices in QBO?.

I'm always around in the Community if you need more help with managing your invoices or anything else related to QuickBooks. I'd be more than delighted to help you some more. Take care and stay safe.