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.
At least for my case, turning on my receiver doesn't turn my TV on, though turning my TV off turns the receiver off, in such cases I just turn the receiver back on again, or never turn the TV on in the first place.
When I turn on my TV my receiver also turns on, but when I turn on my receiver my TV doesn't. My apple TV (connected through the receiver) turns on both. Same goes for off in all cases.
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.