Does atmos as LPCM mat sounds better than DDP?

Depends on the source. If your Atmos is from any streaming service (netflix, apple tv +, etc.) then there is no difference. The streaming services send compressed Atmos (DDP), and Apple TV converts it to LPCM mat. 
 

If your source has trueHD sound (e.g. from Plex) then LPCM, being uncompressed, may sound better. 

Thanks for your reply just one question I have nvidia shield pro and I get atmos true hd using plex will it sound same if I use apple tv 4k with plex true hd source after lpcm update?

Truehd without Atmos = same on either ATV or shield, using plex

Truehd with Atmos = currently with ATV you will lose Atmos. 

Would someone be able to explain to me why the temporary fix would not be as simple as turning off eARC, and setting the TV to auto.  In reading these threads, and trying to process with my limited knowledge, it seems that with the above settings, ATV would then downgrade to DD+ and everything should work fine.  

I have tried this and still do not receive any sound.  I apologize if this has already been discussed, but I am still trying to wrap my head around how some with LG tv’s are getting sound and other are not.  I am sure it must have to do with different models and firmware, but someone much smarter than I am is going to explain it better than I am.

It depends on your TV. Sony, for example, “insists” on telling ATV it can accept LPCM, regardless of audio output mode. I believe the sane is true for LG as of recent firmware versions.

Moreover, I should note that Apple say that they only support Atmos output using LPCM Mat: “Apple TV 4K uses a high bandwidth form of Dolby Atmos that doesn’t work over ARC connections.” (source)

That makes sense.  I was looking at the Apple website and saw that ATV outputs DD+, which led me to believe if eARC was disabled, the format would be pushed out in less than the MAT format.  Thanks for your help.

I’ve never been able to get DD+ out of Sonos Arc via ATV4K.  I am however able to get it via native Netflix app from my TV.  I have a 2019 Q7 Samsung 85” w/ ARC which does passthrough DD+ for native apps.  I can’t wait to get my hands on the ARCANA by HDFury.

I just received an update for our LG Nano91, and I am now able to receive Atmos through the ATV.  I assume it is DD+, but the app is showing Atmos on both the Rooms screen, as well as in the “About my System”.  It looks like we are finally able watch everything through one source!

Are you talking about the Apple TV+ app built into LG TV or the Apple TV 4K?

No change for me with Apple TV 4K. 

I am referring to my Apple TV 4K.  I have always been able to use the LG apps, but this was new.

ok thanks.  I am glad for you .  I have an LG 75 Nano (2020) and it still doesn’t work for me unfortunately.  

that is the TV I have, and the update came in last night.  Have you looked for a new update?  I had to turn the tv off and back on for the update to take affect. The firmware is 03.10.60

oh wow. Thanks.   I see the update for your TV.  I have a LG 75Nano906  and so our updates are just a little bit off time wise.  My model gets the same updates, but it seems to always comes a few days or weeks later than yours.   It was the same when LG rolled out the AMD Sync, in that we got it a few days/weeks later.  It was the same update, so I am really hopeful that LG will be rolling out the update you got to my model in the next few days as I don’t like the internal apps and prefer my Apple TV 4k. 

Watching Greyhound on my Apple TV 4K. 2020 Samsung Q80T eArc set to Auto and Atmos enabled. Here is what S2 is telling me for audio output on my Sonos Arc. 
 

Now when I disable eArc on my Samsung I get this showing in the S2 app. It appears that ATV 4K is sending an uncompressed True HD Dolby Atmos signal your my Sonos Arc based on a comparison of the two screen shots from my previous post. 

What I find interesting is that LG shows the latest update as version 3.10.28 from 8/11/2020. The listed changes are 

1. Improvement  
 1) Support AMD FreeSync 
 2) Sport Alert improvements  

I will have to try my tv later cause I have a similar 2020 model. 

You need to have the newest which is firmware is 03.10.60 according to khazz22 above.  That version shows up on the LG website in the US.   I have the version 3.10.28 you mention and it doesn’t work., so  hopefully they should roll it out soon for 75Nano906NA (Europe).

version 03.10.60 (US) shows

03.10.60] 
1. Fix black screen appear issue when booting the TV 
2. Fix the issue of re-running certain application or rebooting TV 
3. Improvement of the issue where certain BT Audio devices cannot be searched

Here’s the info:

Movie: The King of Staten Island

TV: 2019 LG OLED C9 65 Inch

Connection to Arc: HDMI ARC 

Audio: eARC turned On

Digital: Passthrough 

See screen shots below for other information:

 

 

Thanks for this, what does the app say when you try to play regular 5.1 content (not Atmos) from Apple TV?