it might just be for 4k , I’m not entirely sure
Share audio with a second pair of headphones
You can share audio from Apple TV to two pairs of compatible Apple wireless headphones, such as AirPods or Powerbeats Pro.
For more information on which headphones are supported, see the Apple Support article Share audio with AirPods or Beats headphones.
- Press and hold the Home button on the Siri Remote to open Control Centre.
- Select the Audio Controls button .
- Swipe down to headphones, then select the headphones you want to use.
- If you don’t see your headphones, follow the instructions in Find and connect to a nearby Bluetooth device.
- Select Share Audio, then follow the on-screen instructions to pair the second pair of headphones.
Use Apple TV to play audio throughout your home - Apple Support