It's called "bluetooth". 😉What ever the sensor is called that receives the signal from the remote.
Damn, you're absolutely right. 😳I know for sure that the first gen ATV 4k box has an IR sensor; otherwise, my Harmony IR remote and 3rd Gen Apple TV remote would not work with the unit.
4K Apple TV IR Sensor location - Apple Community
discussions.apple.com
I always thought it was Bluetooth as well until I decided to try my 3rd Gen remote with my ATV 4k.Damn, you're absolutely right. 😳