major problem with Sonos Arc Ultra - Sonos doesn't let switch to other speakers from TV menu

Sonos does seem check in with the TV and re-establish the connection via CEC more compared to other soundbar manufacturers. As Sonos also seems to adhere to the HDMI-CEC spec (as you must have read in the threads you link  to), this might not be identified as a problem. Since Sonos is aimed at less tech savvy (but affluent) consumers this might even be a feature, not a fault. Would it not be possible to turn CEC off temporarily?

The Sonos’ answer to the fact you cannot connect a headphone reliably when you do not turn off CEC on your TV is to use the Sonos Ace’s TV Audio Swap feature.

As is detailed in the other threads the sound output routing is determined by the TV and not the speaker device, in this case Sonos. All Sonos does is let the source, controlling, device (your LG TV) know it is there and ready to use. The TV decides to use it, or not. Sonos is not 'stealing' the sound - just processing what it is given by the source.

This is all as per the CEC specification. Your issue would seem to be with, in this case, LG WebOS and not Sonos... maybe raise it with them?

Would a CEC blocker on the eARC line stop this?

What else would it break?

Since every TV I've used has just worked I'm clueless here.

I just switch off simplink on my LG TV and am then able to switch to other speakers/outputs, or audio inputs - i thought that’s how most TV’s work these days with the (enhanced) Audio Return Channel enabled alongside CEC. On a Samsung TV you simply switch off AnyNet+, just as another example.

If switching off these things becomes problematic- maybe consider using the TV’s Optical output instead to the soundbar, via the Sonos Optical to HDMI adapter. It’s slightly restrictive with some codecs being unavailable, but it may help simplify the switching to other speakers etc.

Another option would be just to power down the soundbar when not required, rather than changing to using an optical connection which restricts available audio formats.

The replies here are making ridiculous outlandish excuses to clearly a problem - that defies common sense, logic and how other soundbars operate.  

Moreover, even turning SIMPLINK (HDMI-CEC) in LG TV menu DOES NOT work properly.  The setting toggles back!! if you try to turn it off, the same way the sound gets restored.  So other than physically disconnecting the HDMI cable or power cable to the soundbar there is no way to shut down sound output to Sonos.  Completely ridiculous. 

Must be the way LG have implemented CEC on that particular TV model - I don’t have that issue with my LG C9 OLED TV, it simply disables and stays that way. Maybe see what LG Support suggest in this instance - there might be something in the TV’s hidden service menu they can (perhaps) adjust for you, or maybe fix it with a TV firmware update. 

The CEC spec is not very tight and each manufacturer uses its own interpretation. If manufacturer ‘A’ is causing issues for one or more other manufacturers they may make accommodations. Unfortunately, at a later date ‘A’ might make some changes that breaks these accommodations.

A CEC blocker will probably help the sound and video issues at the cost of some automation convenience for the user. A user remote will need to be configured to send IR Volume commands to the SONOS soundbar.

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