Earlier quoted context omitted.
Sounds like the hand terminals from The Expanse which you can flick onto any nearby display. Which I dearly would like to see, but the protocol and security implications make my head hurt.
Apple doesn't have the "flick" UI for it, but you can screen share a Mac to Apple TV, so I'm able to use my TV as a monitor with no trouble. The security boundary is that all devices need to be logged into the same wifi, maybe also iCloud.
And that's before you get to the possibility of the gym treadmill screen or coffee shop keyboard or whatever being a hostile device. Which they would easily be if people were going to use the system for something of high value as opposed to casting YouTube to the treadmill screen. Which may be a little bit of a data leak opportunity as it stands, but it's not quite a screencast of your banking account, complete with key log.