I, too, am quite curious on using the Power Apps connector for this and possibly the SendApprovalMail option but don't know what to do with the parameters like NotificationURL in place of where the To: would normally reside.
I stumbled across the same reference site as the only thing out there and nothing helpful.
I'm really surprised I can't find any other inquiries of the same outside of this. The reason for using it directly in Power Apps vs flow? Well, once you've started using the "Office365Outlook.SendEmail" (V2) you realize it's a lot easier than creating a Flow, especially if you're going to have a dozen or so different emails to setup. It's also one less product to integrate in the solution.
My gut tells me these are either not usable yet or you have to build a Flow and put in parameters that reference that Flow so that it is what actually runs. All that said, if both SendApprovalMail and SendMailWithOptions do the exact same thing and have the same limited options as Flow I would still be left missing a piece of the puzzle for my requirement of allowing the approver to approve and send to another approver of their choice (connected to an AD people picker.
