Apple TV Remote won’t control volume or turn on Vizio TV

I tried using CEC, but I don’t think my tv is compatible.

Apple TV would use CEC to signal to the TV to turn on, whenever the Apple TV box is woken from sleep mode (standby). In effect, you would let the Apple TV box turn on the TV (no power button needed per se).

Ask your TV manufacturer if your model supports CEC for this functionality (it would be odd if it didn’t).

What is the exact model of this TV?

CEC should be activated on both the Apple TV box and the TV.

For the Apple TV box: Settings﹥Remotes and Devices﹥Control TVs and Receivers (or*: Turn On Your TV with Your Remote)﹥On

For the TV: See its manual.

Use the Apple TV remote to control your TV and receiver - Apple Support

*Depending on whether there is a receiver in the setup.

I found the manual online, and from what I could find, I’m doing everything correctly.

Here’s a picture showing what I’m seeing. I don’t think my tv is detecting the CEC signals from the Apple TV.

It is possible that some (older?) TVs are programmed to send power-on signals to other devices, but not interpret power-on signals from other devices. Ask the manufacturer to be sure, if a peripheral can wake this TV model through CEC.

From the manual (p.40):

The control panel in the manual looks different from yours. It is supposed to have an on/off (enable/disable) setting, as well as a Device Discovery function. Perhaps this TV model needs you to register a device with the TV first?

*note: I tried switching volume control to HDMI, but the TV wouldn’t respond, so I switched back to TV via IR.

Audio controls over CEC is a specialty function for select receivers (not TVs), and it may be slower than IR, depending on components. Using Volume Control on the TV via IR is perfectly fine, from the Siri Remote directly to the TV.