Apple TV won't turn on my tv

HDMI-CEC has to be supported and turned on, on both devices.

For the Apple TV, that settings is as described on: Control your TV or receiver with your Apple TV Remote - Apple Support

Settings﹥Remotes and Devices﹥Control TVs and Receivers﹥On|Off

Make sure you have enabled CEC on your TV and within Apple TV settings - remotes and devices. If it persists then see below.

HDMI CEC is determined by the TV and each manufacturer has it's own implementation of the protocol. You would need to consult your manual, check if the TV has any further firmware updates and contact the manufacturer if necessary.

As I said above CEC is dependent on the TV and each manufacturer has its own implementation. When issues arise it would be their responsibility to fix it. The options are to consult the manual, check for firmware update and then consult with the manufacturer if it persists

Then please refer to the second part of my post above.