Set your TV to these settings and you shouldn’t have to toggle eARC on/off:

HDMI Input Audio Format: Bitstream

Digital Sound Output: Pass Through

eARC Support: On

Thanks for reply

that is how it is set at the moment.

What happens if you change the Digital Sound Output setting to Auto instead of Pass Through?

Are you only using the TV’s native streaming apps or are you using an external media device?

Hi

if I have earc off the native apps play atmos and Dolby digital plus 5.1 on bbc etc

i need earc on to play atmos from Apple TV 4K but only get Dolby multichannel PCM 5.1 on bbc etc ????

Yes, eARC doesn’t need to be enabled for the native apps to play the proper audio formats.

Are you 100% sure the Digital Sound Output setting on the TV is set to Pass Through and not Auto?

100% been trying different settings all night

With the TV set to Bitstream and Pass Through and eARC enabled, these are the audio formats you should be getting from the Apple TV 4K:

Stereo source - “Stereo PCM”

5.1 source - “Multichannel PCM 5.1”

Dolby Atmos source - “Dolby Atmos”

Hi 

this is exactly what I get on the tv itself with just tv and Sonos connected, is that correct?
Apple TV with earc on gives atmos, off it gives Dolby digital 5.1.

With the TV set to Bitstream and Pass Through and eARC enabled, these are the audio formats you should be getting from the TV’s native apps:

Stereo source - “Stereo PCM”

5.1 source - “Dolby Digital Plus 5.1” or less often “Dolby Digital 5.1”

Dolby Atmos source - “Dolby Atmos”

What should it be on terrestrial digital television in the uk? Toggling earc on and off changes to that in my first post

I don’t live in the UK so I don’t know exactly what audio formats they use. If I had to guess:

Stereo source - “Stereo PCM”

5.1 source - “Dolby Digital 5.1” or “Dolby Digital Plus 5.1”

Thanks

which is better dolby multichannel PCM 5.1 or dolby digital plus 5.1 or is it subjective?
can you tell the difference?

If you are seeing “Dolby Multichannel PCM 5.1”, the TV is probably doing some sort of audio conversion which you don’t want. That’s why the Pass Through setting on the TV is the best option because it leaves the audio untouched. “Dolby Digital Plus 5.1” is what you want to see. But choose the audio format that sounds best to your ears.

Most UK terrestrial channels are in stereo. Surtound sound is a distant dream in most cases. 

I have been watching World Cup matches on iPlayer as this gives the option to watch in UHD. I haven't paid any attention to the sound format. 

Basically I get Dolby Multichannel PCM 5.1 when earc on and Dolby Digital Plus 5.1 when toggled off , not sure why ?  That’s just the tv and Sonos arc connected ???

Me too, the sound on bbc hd is 5.1 but iPlayer is stereo, but it’s football so who cares and the picture is much better

Fixed- use settings discussed above (earc enabled/bitstream and pass through) but also change sound mode share to ‘enjoy Tv sound mode’ this will show Dolby digital 5.1 when 5.1 is sent to Sonos product or Atmos when atmos. 
I am using LG pled C2 + Beam(2) sub(3) and 2 sonos one + Apple TV 4K