Why can’t I turn on control TVs and receivers in my Apple TV 4k

That will be based on HDMI CEC, which is dependent on the TV or receiver. Each manufacturer has their own implementation and it would be up to them to fix any issues that occur. You can refer to the manual for troubleshooting, check for a firmware update and contact the manufacturer if necessary.

Please refer to https://support.apple.com/en-us/HT205225 to learn Control your TV or receiver with your Siri Remote or Apple TV Remote