Some TVs send CEC commands through the HDMI ARC/eARC even when powered off (not unplugged).
Refer to the TV's user manual to disable settings (Idle TV Standby, Remote Start, etc.) that send CEC commands when the TV is on Standby. Also, upgrade the firmware of the TV to the latest version.
Alternatively, unplug the power cord of the TV. (Powering off using a remote only puts specific TVs on Standby and is not recommended – completely turn off the power by unplugging the power cord)
For example, these are the steps to modify settings in a Sony TV:
- Press the Settings button on the TV remote to launch the Quick Settings
- Select Settings
- Power > Idle TV standby > Off.
- Network & Internet > Remote start (disable)