Hopefully by now you've figured out the issue with TCL Roku TV and AppleTV App.
If not, I had a similar problem. AppleTV app had been working with my configuration for over a year and then suddenly stopped streaming and the "Video not available" error was displayed. AppleTV app was accessible on iPad and iPhone in my network and other streaming channels worked on the Roku TV.
My configuration uses the Roku Streambar as speakers, not as a streamer (I owned it before buying the TCL Roku TV) because the sound is much better than the built-in TV speakers.
My TV is also configured to "Fast Start" so it really never shuts down, just goes into a sleep mode.
To resolve the issue I "Re-Started" both the Roku Streambar and the TCL Roku TV from the System Menu on the Roku TV.
If you don't have a Roku Streambar, just do a system restart on the TCL Roku TV.
To restart Roku Streambar go to menu: Settings > Remotes & devices > Speakers > Streambar> Restart Streambar
Then to restart the TCL Roku TV go to: System > Power > System Restart
After both restarts, AppleTV app is working and streaming normally.