Situation:
Smartphone is connected to tv.
App's job:
Nothing that appears on the smartphone appears on the screen (the screen is black).
When the user clicks a certain button inside the app, the screen of the smartphone is shared on the tv screen, and everything on the iphone screen can be seen on the screen (horizontally).
If you contact me, mention how long it would take you to finish the project, and more details will be given in private.