Hey all, just wanted to share how I found out how to get 5.1 to turn off in stadia when playing via chomecast. In my experience, the 5.1 audio is laggy and has a tinny sound to it. To get stadia to output stereo, go into your Google home app, click on your chromecast, scroll to surround mode and change it to stereo. This will disable 5.1 on stadia when playing on the chromecast.
I also recommend:
Turn off:
Until Av1 codec only activates 4k