Any equivalent to SP2010's "Impersonation Step" in PowerApps/Flow?

It is possible to send an email from the Microsoft Flow system account. Likewise, if you are given delegate permissions in Exchange to send on behalf of another user, you can configure your flow to do that. Third, you can set up a Shared Mailbox in your tenant to send the email (if you don't want to use a person's email but also want the email to come from your tenant not from "Microsoft Flow"). I hope this helps!