You have the HDMI cable from the ATV plugging into the TV’s eARC port - correct?
Test with a different HDMI cable if you can - it needs to be certified TV to AV and AV to Apple TV - Bellini 4K is one example
Restarting the tv and ATV might help.
There are several settings you can turn on with your Sony to sync with Apple: Your settings might vary according to your model
- In the Sony settings - System - AirPlay & HomeKit needs to be enabled.
- On the Sony settings - Channels & inputs - External Inputs - HDMI Signal Format - eARC>enable Dolby Vision - Also in this same set of settings enable in Bravia Sync Control - On
- Now turn on your Apple TV and it will ask if you want to use Dolby Vision, click ok if you agree .
- Then go into settings Audio Video - Audio Output - Make sure HomePods are set to default audio.
- Under that setting is ARC (Audio Return Channel) - Enable that (this won’t enable until you enable Dolby Vision)
- On the Apple TV - Remotes & Device’s - turn on Control TVs and Receivers so you can control both remotes/Devices and under that setting is Volume Control - choose Auto.
Use HDMI ARC or eARC with your Apple TV 4K - Apple Support
If you can't control your Apple TV with your home theater or universal remote - Apple Support
