Casting

From what device with the Apple TV app did you intend to stream?

What is your model TV?

Apple apps on Apple devices can stream to other devices using AirPlay, not other casting protocols. That means that the receiving device must support AirPlay too.

Select newer models TV may support AirPlay. List of AirPlay 2-enabled smart TVs and third party TV-connected devices - Apple

Apple’s own Apple TV set-top box supports AirPlay.

Alternatively, select newer smart TVs may support the Apple TV app natively among their smart apps.

Or you can use a HDMI-connected streaming device that has the Apple TV app.

List of Apple TV app-supported devices - Apple

All the ways to watch in the Apple TV app - Apple Support

Watch on your TV

• Apple TV (4K, HD, and 3rd generation) ﹥

• Smart TVs ﹥

• Gaming consoles ﹥

• Streaming devices ﹥

If you have AirPlay support in your TV or in the streaming device connected to your TV, then either use the in-app AirPlay symbol, or use the Screen Mirroring tile in Control Center.