For some reason, GPU makers don't usually expose the CEC interface for the HDMI ports on their cards. Even the raspberry pi's ability to support it wasn't standard/default for years.
The common workaround if you had a kodi PC or something was to buy one of these things: https://www.pulse-eight.com/p/104/usb-hdmi-cec-adapter and run a HDMI cable through it. Because CEC is open drain like i2c is, connecting to it anywhere in your network of devices should work. (the HDMI spec mandated that the CEC pin needs to be connected, even if you aren't using it, from the first version) Just connect it to a spare HDMI port anywhere and you're off to the races.
It's cool that that exists, and also feels silly to spend $50 + need to buy/run an extra HDMI cable just to make your TV turn on when your device does.
Real shame these gaming-tailored devices don't support it natively. I wonder if the DP vs HDMI licensing battle is involved.
The common workaround if you had a kodi PC or something was to buy one of these things: https://www.pulse-eight.com/p/104/usb-hdmi-cec-adapter and run a HDMI cable through it. Because CEC is open drain like i2c is, connecting to it anywhere in your network of devices should work. (the HDMI spec mandated that the CEC pin needs to be connected, even if you aren't using it, from the first version) Just connect it to a spare HDMI port anywhere and you're off to the races.