Hi gennieosg,
I also like the idea of seeing some sort of warning that an invoice is connected to an estimate before you can void it.
Apparently, the current warning we can see says that there are one or more payments connected to the invoice, and not about having a connection to an estimate. For this reason, I recommend sending your suggestion by clicking on the Gear icon and selecting Feedback. That way, our engineers can consider adding one in future updates.
On the other hand, you can check out the Training menu above if you want to see some video tutorials for QBO.
I'm just a comment away if you have questions about QuickBooks. Take care and have a good one!
