Apple TV don't show video on secondary display.

Commercial titles will have a HDCP requirement. That mean that the display and connection must support HDCP as well. Please specify the make and model display, and how it is connected.

Hello and welcome to Apple Support Communities, O1eg!

We understand you're seeing a black screen when trying to play a video on the TV app while using a secondary display. We'd be happy to provide information to help you address this.

Try the steps here to troubleshoot the external display connection:

Get help with video issues on external displays connected to your Mac

If with those steps it still won't play correctly, try playing the video while in safe mode: Start up your Mac in safe mode

If it plays correctly in safe mode, try restarting as normal and test again.

Let us know the results.

Have a great day!