There are some smart televisions which are only smart after they’ve been turned on. I don’t know if that is your situation or not.
I have a different model TV which has that issue. I added a SwitchBot mini IR blaster, which has an official smartthings integration. That lets me turn on the TV with an automation, and after that I use voice controls.
You do have to buy the extra device which usually costs about $40 depending on whether it’s on sale, so I don’t know whether you would be interested in that or not.
Anyway, if you do that the TV power button ( actually the SwitchBot) does show up in automations, so you can trigger off of it.
Here’s the discussion thread on that option. (The topic title is a clickable link)