The LG CX series TV is equipped with HDMI eARC so it does work with the Sonos Arc. But some CX owners have experienced some issues with the Arc. If you search “LG CX Arc” in these forums, you can read about some of the issues people have experienced.

Since the updates in January, I know I haven’t had any problems at all.

I’ve got both and as good a quality as the sound is on the Arc, and the picture quality of the LG CX, the delay is pretty distracting with lip sync, even with the most recent updates.  I use EARC, with a high speed HDMI and the problem is the LG I think.  There’s no way when you adjust the lip sync in sound settings to go into the ( - ) negative of sound delay, only positive.. so it’s either a little out of sync… or really out of sync if you prefer pushing it up the scale… LG really need to get on to it but it sounds like that’s been the case for ages even a couple of TV models ago..