If the volume buttons on your Apple TV remote suddenly stop controlling your television or soundbar, the Apple TV itself may still be working perfectly normally.
Volume control can be handled through HDMI-CEC or infrared depending on the equipment in your setup. If a TV, receiver or soundbar changes input behaviour, loses HDMI-CEC settings or stops responding to the remote’s IR signal, volume control can fail while navigation continues to work.
Start by checking Settings on Apple TV under Remotes and Devices. The Volume Control option can usually be set to Auto, HDMI or a learned infrared profile depending on your hardware.
If the remote used to control volume correctly, restarting the Apple TV and the television or soundbar can also restore communication. It is worth checking HDMI-CEC settings on the television too, as manufacturers often give the feature their own brand name.
For infrared setups, make sure nothing is blocking the front of the TV or soundbar and that the remote has a clear line of sight.
If only the volume buttons have stopped working while the rest of the remote behaves normally, there is a good chance the problem lies with the control method rather than the Siri Remote itself.