Apple TV HDMI CONTROL not working

troubleshooting steps I would take would be around the line of

turn hdmi-cec off pull the plug on all equipment

let them start up again

turn hdmi-cec on again on all equipment and test

check if there are newer firmware for tv and appletv box and so forth

I have very similar problem to yours but with simpler setup. I have just a TV as a receiver for everything, AppleTV, PC, PS5. And additional IR controlled audio amplifier. tvOS 18, and it is way worse than on 17.4

The issue is that CEC basically stopped working properly. Yes, I know powercycling, resetting do defaults etc. etc. and favourite "solution" - change the cable. I did it all.

The only thing I can only do with Apple TV is ... to turn the TV off. Nothing else. Turning on? Not at all. Any other CEC-related controls? Not at all. It is even worse, pushing the "back" button on the TV remote is not acting as a "return back" or "backspace" but it is switching the TV to the first possible HDMI input, to which Apple TV is not connected.

I see no solution to this so far other than to completely disable CEC control or use any "hardware CEC proxy" or something but this would be overkill....