I haven’t tested this enough to know if it’s a real hidden feature, or just me placebo-effecting myself, but I swear it takes way less time to wake up my TV (Samsung) if I press the little TV button on the ATV remote 5x really fast.
Like if I press it once, the ATV wakes up and usually the TV does, but often showing the wrong source. 5x fast consistently wakes the TV to the right input.
Oh? My Apple TV 4K (2021) turns on the TV and receiver when I start AirPlay, and the receiver switches the input to the AppleTV if it wasn't already on it. This works whether the TV+receiver were on or off. My TV is a Sharp from ~2013, and the receiver is a Yamaha also from around the same time.