My Samsung TV is a similar age, but menu setting names might be slightly different. I have the same setup and can play Atmos. My settings:

TV:

Settings / Sound / Sound Output: Receiver (HDMI-eARC)

Settings / Sound / Expert Settings :

• HDMI-eARC Mode: Auto
• Digital Output Audio Format: Pass-through
• Dolby Atmos Compatibility: On

Settings / General / External Device Manager / Anytime+ (HDMI-CEC): On

Settings / General / External Device Manager / Input Signal Plus: ON FOR ALL HDMI INPUTS!

Apple TV

Settings / Video and Audio / Audio Format: Dolby Atmos On.

Also ensure the content you are playing is actually in Dolby Atmos, and that the streaming subscription you have is premium enough to include Dolby Atmos.

One more thing - check your HDMI 2 port is HDMI 2.0 and not HDMI 1.4 (if not, swap to an HDMI port that is), AND that you are using a High Speed HDMI cable - both are essential for Dolby Atmos. 

The sonos Arc is connected to ARC port and the apple TV to HDMI 1 the content that I watch on netflix support dolby atmos but still The apple TV is not playing dolby atmos just playing dolby surround sound 5.1 

Did you see my earlier reply, not just my last one? Have you compared settings?

I did see you reply I checked everything and this is my TV settings

I’d try changing PCM to Bitstream. 

I can only choose these two options. I Can’t choose dolby digital+

And just to be clear - all the other settings I posted match on your TV (eg Input Signal Plus, etc)? 

Yes all the settings are the same 

One final question - are you using the Sonos HDMI cable for the ARC, and are you using a high-speed HDMI 2.0 cable for the Apple TV?

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’?

No Just Auto without atmos :(

?

One thing you didn’t answer about the Apple TV settings. I said: 

“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.”

Were you actually presented with the option set Dolby Atmos to ‘On’?

Its just auto there is no immersive audio it’s not showing 

I just found the answer on Apple’s site.

For Dolby Atmos, your Apple TV 4K needs to be plugged into a TV with an HDMI eARC port - unfortunately an HDMI ARC port will not cope with the bandwidth required for the sort of Dolby Atmos used by Apple TV. 

So what you are getting from your Chromecast must be a lower bandwidth Dolby Atmos, which your HDMI ARC port can cope with. 

Sorry it’s not better news but after all that, you can’t have Dolby Atmos on the 2019 Serif...