The HDMI ARC is for sending audio from the TV to the audio device, in this case the Yamaha Soundbar. The Roku is plugged into a regular HDMI input. In addition to the HDMI ARC, each device has to recognize each other as a hdmi-cec device. If the tv settings can't refresh the cec devices connected to it, you'll have to unplug the power from each wait a bit and then plug it back in, give it time to recognize each other. It won't be instantaneous.
The HDMI ARC is for sending audio from the TV to the audio device, in this case the Yamaha Soundbar. The Roku is plugged into a regular HDMI input. In addition to the HDMI ARC, each device has to recognize each other as a hdmi-cec device. If the tv settings can't refresh the cec devices connected to it, you'll have to unplug the power from each wait a bit and then plug it back in, give it time to recognize each other. It won't be instantaneous.
I tested this out multiple times with no change. Still no audio
Ok..it’s working now. I unplugged everything after putting all audio settings back to auto. Plugged in tv, soundbar, and Roku. Restarted the Roku for good measure, turned on the soundbar after noticing it was off and it worked. 😁
Ok I spoke too soon. During setup I was able to get it to work, but the next time I hit power on the remote the audio was off again. I looked at Settings and saw that the remote was set up as IR not CEC. I had configured it for HDMI/ARC/CEC but the Roku device configured it for IR anyway.
There was a disclaimer somewhere in the documentation that not all tvs will be recognized as CEC capable.
I called the support desk and was told it wasn't a Roku problem and to talk to LG. (Really?)
I have spent way too much time on this and have given up. I bought a Chromecast and it configured no problem. I really wanted Roku to work, like the interface and features, but oh well. 😞