<!here> curious, has anyone setup an approval workflow that supports a 'Reject with Note' function/action? .. Native Invoice approval only allows the user to reject an Invoice, requiring a subsequent action to relay the reason why the Invoice wasn't approved.

You can create workflow and suitlet combination to do that. Zone and company has a bundle similar to this for vendor invoice

I actually was able to implement something resembling a Reject with Note - two work flows, one Custom Record (Rejections). Custom Record fields: Reason, Transaction (is Parent), Created By & Rejected By. WF#1: Action on Rejection State = Go To Record > Rejections. Approver enters comments re Rejection in a Long Text box > Save. WF#2: Record Type = Rejection; Sets field values for Created By & Rejected By, Go to Record to redirect Approver back to the original Transaction, and email notification to Created By, from Rejected By, with the {reason} value in body. @jokell