compressed dolby atmos over Arc from ATV4K

What specific model Samsung TV do you have? Is it equipped with eARC?

No just arc 

In most cases, the Apple TV 4K requires eARC to play Dolby Atmos audio. You need to use a different streaming device like a Roku Ultra or Fire TV Cube or use the TV’s native streaming apps instead.

I‘m pretty sure that also won‘t work if the tv though equipped with hdmi ARC doesn’t support Atmos at all. To get compressed Atmos from any device (indeed including AppleTV 4k) via hdmi ARC the tv also has to support the Atmos format. A few tv models (for example some from LG) do so.

Not sure how that is possible with AppleTV because it normally needs eARC because of MAT format, but @skullc confirmed he can use Atmos from his AppleTV on his Atmos capable LG tv that only has ARC. 

So the tv native apps worked

If tvs native apps work with Atmos, the tv does support the Atmos format. So compressed Atmos should also work from other sources like FireTV 4k etc. - And, as another user confirmed, also from AppleTV. 

I suppose it depends on the content you play. What movie, streaming service and audio track (also what langue) did you try?

How are audio settings on tv and AppleTV?

As I’ve already mentioned, OP’s Samsung TV doesn’t support Dolby Atmos audio on the Apple TV 4K. They need to use a different streaming device that doesn’t use Dolby MAT or just use the TV’s native apps.

@GuitarSuperstar

That‘s what I also was already thinking… 

But then I saw posts, latest from @skullc two days ago, where users confirmed Atmos from AppleTV working via ARC (without e) connection of an Atmos supporting tv. 
So if ops samsung tv supports Atmos, shouldn’t it work!? 

If Atmos on ops tv ONLY works for native apps on tv, it probably won’t support Atmos passthrough… (what I can’t imagine) and Atmos wouldn’t work from any external device including FireTV etc. 
 

Strange… 

@Schlumpf

its compressed atmos as in Dolby atmos (dd+)

to be accurate 😊

Yes, I know… 😉

But I see no difference between your setup and ops over here. 
AppleTV 4k, Atmos enabled tv with just hdmi ARC. 
So why does it work for you and not for him? 
Before I read your posts I always thought (like @GuitarSuperstar ) AppleTV 4k always needs eARC because of Dolby MAT.