I just bought a new Sonos Arc and LG 65OLED65AUA tv. Everything seems OK but I am having problems with sound from my Apple TV 4K (latest version). I only get sound when Dolby Atmos content is played, no sound with Dolby 5.1, HD, etc. I spent and hour with Sonos phone support yesterday. We were unable to find a solution. I tried different settings on the Apple TV and LG tv. Today I turned off the eARC setting on the LG tv and now all is working. I think with eARC there is more information transferred with ARC and there might be a slight difference in sound with Dolby Atmos. The eARC was turned on automatically when I installed the Sonos Arc on the LG tv. Just curious why the eARC setting seems to fix the problem. Thanks.
Sonos Arc, Apple TV 4K and eARC setting on LG OLED C3

Best answer by GuitarSuperstar
Set the TV to these settings:
HDMI Input Audio Format: Bitstream
Digital Sound Output: Pass Through
eARC Support: On
Set the Apple TV audio settings to this:
Change Format: Off
Dolby Atmos: On
Then do this:
Disconnect everything from the TV and unplug the Arc, Apple TV, and TV from power for a couple of minutes. Plug everything back in but keep everything disconnected. Make sure Simplink is enabled in the TV settings. Run TV Setup in the Sonos app and follow the app instructions. When the app instructs you, connect the Arc to the TV’s HDMI eARC port using the Sonos-supplied HDMI cable. After the Arc has been successfully connected, connect the Apple TV to the TV.
Enter your E-mail address. We'll send you an e-mail with instructions to reset your password.