There should be an option to toggle whether the TV should turn OFF or turn on Art Mode when an active HDMI source goes on standby/powers OFF.
Yes, you can click power OFF on remote, but I’d prefer not to use remote at all. Two examples
a/ Gaming console is put to rest using game controller, the TV simply says “no connection on source” and turns OFF after few mins.
b/ Using TV as a monitor, you disconnect your PC/Unplug your laptop HDMI & TV just turns off after
in either cases desirable outcome is Art mode instead of turning off.