We can send Skype messages via Flow but are unable to send private messages via Teams. Since Microsoft is migrating to a unified Chat experience anyhow - why not add an action that sends a message to one (or all) of the MS chat experiences?
From a PowerApps, send a message to a user via Flow. That message creates a private message between the sender and recipient in Skype, Teams, and StaffHub. This makes it MUCH easier to create flows depending on which applications a company has deployed to their user base.