I'm pretty sure it's a hardware feature of specific graphic cards. Not every HDMI port has that capability and most consumer GPUs don't have it. That's why the GPU on the Steam machine is so important. It has the CEC capability out of the box.

I have a similar setup to you, but I'm running bazzite. I got around it by putting my TV (offline Hisense Roku) into a power saving mode that essentially shuts the screen off and puts it in standby. Whenever there's a change in signal, the display kicks on. However that also isn't a feature on every TV.

It is rare that a computer have HDMI-CEC natively.
Try the command "cec-ctl" (which is part of v4l-utils) or take a look at the Arch Wiki.

Even if your hardware doesn't support it, you can still use displayport with an adapter or even a usb+hdmi adapter.

You'll need a Pulse8 USB CEC adapter.

I think you can buy an adapter