That’s interesting. I have occasionally been annoyed that I don’t have an easy way to play audio from my phone to my home theater audio system without having the TV on. If I turn my TV off it automatically turns my receiver off, and the only way to disable that would also disable turning the TV and receiver on automatically which is a crucial flow.
There might be a way to build a little HDMI CEC controller that could block certain control sequences, but I haven’t looked into that yet.