I've recently bought a mi Android TV 4A, I just want command using Google Assistant my TV when it is turned off. I've also noticed that is impossible to get linked using Chromecast connection if my TV is off, Google Assistant is not able to reach the device. So, in other words, if the TV is off , it is dead. I have been using Chromecast for years and I am able to do that (thanks to HDMI-CEC), and I just want it behaves like an external Chromecast device. It is possible to achive that? Thanks.
The Mi FAQ suggests there’s a CEC setting you could try — on the miTV stick, at least, don’t know about other models. https://www.mi.com/in/mi-tv-stick/faq/
Please look through the settings to find wake options. I found a wake on cast option in my Vu (Hisense) TV that is quite useful. The TV is available as a cast option even when turned off.
Edit: just found instructions for Mi TV 4s, which may work for the 4a too: https://www.reddit.com/r/googlehome/comments/e5pqmc/google_home_cant_turn_my_android_tv_xiaomi_4s_on/ . It seems that developer mode will need to be switched on (as per the comments).
I had this issue with my Philips Android TV, there's an app you can use which keeps the TV when on standby out of deep sleep, I have not needed it lately due to a firmware update and it will use more power on standby.
Sometimes....
My Google Assistant is very inconsistent with that. Sometimes it works just fine, then the next time it will tell me I need to specify which device or say that feature isn't available. Same with turn off command. When I try again saying "turn on/off Device Name" it says it can't do that.
A new bug related to that, that just popped up recently is that it will give a verbal confirmation or noise but it won't turn on the TV.
It's wildly inconsistent.
No... It won't be possible without an external stick as the TV totally turns off the WiFi module (as I understand) when powered off. Only way is to keep the TV in standby/sleep mode, if your TV allows that.