apple tv 4k + sonos arc + samsung serif

For the Sonos I’m using the original cable which is included in the box for apple Tv I’m using UGREEN HDMI Cable 4K 2M HDMI 2.0 18Gbps High-Speed 4K@60Hz HDMI to HDMI Video Wire Ultra HD 3D 4K HDMI Cord Braided Compatible with MacBook Pro UHD TV Nintendo Switch Xbox Playstation PS5/4 PC Laptop

The only thing I can think - as you don’t seem to have a Pass-through option in your sound settings - is that your 2019 TV doesn’t have the capability to pass a Dolby Atmos signal from an external device (e.g Apple TV) to the soundbar, but might be able to send a Dolby Atmos signal from its built-in apps.

Can I ask you to try logging into the TV’s in-built Netflix app (not on the Apple TV) and play Dolby Atmos movie or TV content that way? I would imagine the Dolby Digital+ setting will then become available to you, and you should then see Dolby Atmos showing on the Now Playing screen in the Sonos app. 

I’ve a strong suspicion it’s that your TV lacks pass-through capability, so you might have to just use your TV apps for such content. 

I tried the built in Netflix app on the TV dolby atmos was there And I tried Google Chrome cast. Also Dolby atmos s was played. The issues only on Apple TV 4K

Okay, that’s positive that Chromecast gives Atmos (as that is via HDMI, like the Apple TV is…). So:

On the Apple TV, go to Settings / Video and Audio / Audio output. It should show default audio output as being Receiver Speakers?

The audio menu option Audio Mode should be Auto.

The audio menu option Audio Format should say ‘Auto, Atmos Available’, and when you go into this option Dolby Atmos should be On.

Is anything different for you?

These are my audio setting in my apple tv I changed the Audio mode from 16 bit to auto but the audio. Format is still on dolby digital 5.1

Great, thanks.

Keep 16 bit off, leave it Auto.

In Audio Format, go to Change Format and select Off.

This should then give you the option Immersive Audio, where you can set Dolby Atmos to On.

Fingers crossed!

I did what you asked for but unfortunately still there is no dolby atmos :(

Did the last Apple TV setting give you the opportunity to select Dolby Atmos ‘On’? 
If so, now turn off your TV, Arc, and Apple TV at the wall.

Turn them back on, one at a time, as follows:

    TV - let is fully boot up.

    Arc - let the light settle down 

    Apple TV.

Then go into Netflix and see if it is now showing Dolby Atmos. 

Still no atmos 😭

Oh maaaaaan. 
To check - does Audio Format in the Apple TV menu now say ‘Auto, Atmos available’?