I’m sorry I wish I had an direct answer - Personally I always run an Ethernet connection to my streaming devices which includes my TVs unless I just don’t care about quality (like in the guest room). There are a lot of variables when it comes to wireless connections. I just find going straight to the router works best for me. Have you tried that? No promises but it will give you the best possible thorough put. 4K sucks a lot of bandwidth. 

I have this same Samsung TV and just received the Arc today.  It setup beautifully, and sounds great (with a couple of rear Sonos One SL speakers….Sub on the way).  I originally had the same question as the original poster, but I just streamed Jack Ryan on amazon prime (using the Samsung TV native app) as a test. Dolby Atmos didn’t appear on the Now Playing  screen. I went to Settings > About my system on the Sonos app, however, and I saw Dolby Atmos as the audio input to the Arc. When I went back to the Now Playing screen, Dolby Atmos was there….go figure. 
 

so, it looks like Dolby Atmos can stream from the native apps on this Costco Q8DT!

I have the q95t and I have my Arc wired straight into hdmi 3 (eARC) the Arc only shows the Arc as a HDMI Receiver as opposed to Receiver eARC - I have a horrible audio delay when using Atmos on my Xbox One X and I think a possible fix could be to enable audio pass through on the TV but this is only possible on eARC devices, which for some reason it doesn't seem to think the Arc is. Does your Q80T display the Arc as HDMI receiver or HDMI eARC?

Thanks

TV shows “Receiver (HDMI-eARC)”

I have the same TV as the OP, ARC, Two SL1’s and Gen 2 Sub and have had no issues with Atmos playback and content from Netflix or Prime Video.

Planning to get the same combination Q80T with Sonos Arc. Kinda afraid because i am reading several problems with 2020 Samsung QLED with the Arc.

@Jackh 

Did you get your problem solved? 

Otherwise i don’t have to buy an e-ARC TV if it does not work. Thinking about the LG 2020 Nano series instead. 

Can I ask, are any of the users above including the OP getting any sound out of the ARC when HDMI-eARC Mode is set to Auto.

We have identified an issue where no sound is present through any source once eARC is set to Auto.

Can you confirm please?

In response to your original post, DD+ is translated to Atmos (compressed) via HDMI ARC on limited content on Amazon prime such as Jack Ryan (only season 1). Apple tv and Disney as direct apps built into the Samsung tv do not output Atmos. Netflix as an internal tv app does output Atmos where content allows. 

I believe the external Apple TV device is the way to obtain Atmos on Apple Content.

eARC enabled should allow sound from compressed and uncompressed sources such as Dolby TruHD Atmos as found on 4K UHD Blu Rays etc

Hope this helps.

On my set up I have eArc enabled, Atmos enabled. I am watching Netflix  Night  on Earth and the app is indicating Atmos. If I turn eArc off the app shows Dolby Atmos (Dolby Digital +).  I purchased my TV 10 days ago. 
 

Here are screen shots of the Sound Setting on the Samsung. 

Thanks that's useful - different firmware in the us vs uk

Besides the different Firmware, US vs UK, some have pointed to the One-Connect box as the problem. I assume the Firmware addresses the eARC differently in Built In vs One-Connect.

Man I had the same issue!!! Same tv same setup spent 6 hours with Samsung support and Sonos support and they blame each other, THERE IS NO FIX! it’s just that the tv doesn’t support eArc other than the Samsung soundbars, they even released an update 2 days ago and it doesn’t fix the issue!! $5k tv and $3k sound system, good job sonos and Samsung 

It appears the One Connect Box is the issue with eArc and the Arc. My 2020 Samsung Q80T and Arc are working flawlessly together. 

So what return the TV? I can’t get the HDMI ports on the TV as there is no furniture close to the TV to put all the equipment and its 75 inch!

I don’t have a solution for you. I’m just relaying what I believe is the issue. I live in Canada. Samsung doesn’t provide the One Connect Box  with their sets here. It’s clearly something that Samsung needs to sort out. 

I downloaded the Dolby dignity file Amaze In Lossless form and when I try to play it, it says ‘unsupported feature’ … I have the picture but no sound. I have the Arc, sub and surrounds with a new Samsung 55” QLED TV. Any help?  

Do you have a One Connect Box on your TV? If you do then that will be your issue for it not playing. You will have to turn off eArc in your sound settings and then you should get Atmos played via DD+. But it won’t play that trailer you’re wanting to play as it is likely done in True HD which I believe requires eArc. 

I’m U.K. based and Do not have a one connect box. My arc is plugged direct into the dedicated Arc HDMI port. 

My settings are a couple of posts above. Have a look and make sure yours are set the same. 

Yes I copied you hoping it would work. Should Disney plus come out in Atmos? 

I don’t have Disney +.  When I use the Apple TV Plus app I am only able to get DD+ with eArc off or 5.1 Muti Channel PCM with eArc on. 

I got it working! So I made 2 mistakes, I first downloaded the Dolby trailer earlier from the official link but used the ‘for mac’ download and it didn’t work on my TV. I then downloaded it from an unofficial site that had lots of trailers and could only get the picture to work. I suddenly thought I should have downloaded the PC files from the official site onto to my USB. I did that and I just had Dolby Atmos activated and confirmed in the Sonos app. Sounds amazing. One thing, my rear speakers are on stands behind my sofa … I’m sure it would sound even better if the speakers were above my head (or if the sofa was more forward, which I can’t do).

I may look into wall mounting the speakers.

Good to hear you got it working Moniker.

Enjoy. Do you have the Sub?