Do you mean you’ve read all this? Audio hardware and software configuration
passthrough should be ON. Channels depends on whether the Pi is connected directly to the Sonos (better - 7.1 is OK) or to your TV (probably need to set 2.0 and AC-3 transcode)
Update: I see the Arc doesn’t have HDMI in and the LG doesn’t do eARC. You do therefore need to set channels to 2.0 and engage ac-3 transcode.