After tinkering around for hours, I finally got the deck to power on the TV/AVR simultaneously. This only worked for me with the official Steam Dock. As of now, the CEC settings which are in Beta/Developer mode in Steam>Display, are not available in the stable build until they release it so you will have to run your deck in beta mode. The issue I had with this dock was it was not displaying well/had issues connecting through the AVR. I finally found out that I can plug the deck directly into the back of the TV HDMI port instead, and the audio will still come through the AVR speakers. The CEC also works perfectly so if your TV is off and you turn on the deck with your controller(bluetooth mode only) the deck wakes up and turns on the TV automatically. Also my TV remote controls the deck as well which is great. So all in all, if you do my steps above it will work.This is how to do it:

1. Connect your deck to the steam dock but do not plug the dock to any TV source just yet

2.. Steam button> System> Enable Developer Mode.

3. Steam button> System > Beta Participation> OS Update Channel > select Preview

Steam button> System > Beta Participation> OS Update Channel > select Steam Deck Beta

4. It will ask you install/update/apply updates to the steam deck it will also ask you to update the dock as well in beta mode, make sure the dock is connected to the deck.

5. Once everything is updated, go to Steam button> Display > CEC > click both the Enable HDMI CEC support and Wake TV when device resumes from sleep

6. Turn on the TV and then plug the HDMI cable from the dock to the back of the TV HDMI 4K input (in my case there is a 120HZ HDMI input, so pick your highest hz input if you have one).

7. The deck screen will likely go black and try to feed video, switch your input to HDMI source your deck is plugged into, if not it will when you switch sources. You should now see your screen on the TV and the AVR will auto switch and sound should come out of your speakers.

8. Lastly, you may likely need to tweak a TV setting. I have seen couple posts about LG TVs that there is a setting you should enable. "LG c2 TV I was using that in the "device" settings of the TV, you need to turn Deep color for HDMI to off". In my case on the Sony, I had to go to Picture Settings> HDMI Sources > pick the one HDMI where the deck is plugged into and make sure its profile is Standard Profile not the VRR one.

After powering it on via blueetooth controller, the deck wakes up the TV & the AVR no problem. You dont need any HDMI CEC adapters after all.
https://www.youtube.com/watch?v=-QSo4H4OCcw