I had previously attempted to get help with this issue but I realize now that I misstated the problem so here goes…
I have an LG OLED65B8PUA tv, Denon AVR5400BT receiver and Roku Ultra. The HDMI out from the receiver goes to a TV HDMI in just for the video. The ROKU plugs directly into the receiver, not the tv.
I had been using the Roku remote which turned on/off the tv and receiver and controlled volume with no issues. After an update to the Roku a few months ago, the volume stopped working. I misstated that this was a ARC issue but after doing more research, realized it is an CEC issue.
I just tried a factory reset to the Roku and TV, unplugged everything and set up each component one by one. I got everything to work with the Roku remote just as it had before when but I turn everything off and then back on, the problem comes back. This definitely has to be a settings issue with the Roku. Yes, CEC is turned on for all devices. I tried the IR menu from the secret Roku menu but am I sure of the exact steps to take there.
I feel like I’m so close to getting this to work now that over ruled out settings on the tv/receiver, cables, etc.