Not all Dolby Digital plus signals are Atmos.

@Remy de Fromage No, you are just playing Dolby Digital Plus audio. When you are playing Dolby Atmos audio, the Sonos app will display the Dolby Atmos logo.

Thank you, question answered

I apologize, but I would like to know why if the streaming service declares the audio output in Atmos I see the signal in dolby digital plus 5.1? I am connected with HDMI eARC cable directly to the TV.

What streaming service are you using? Are you playing the ORIGINAL language audio track? What model TV do you have?

I'm using Disney plus, the track is in Italian and the TV is a 2020 Samsung Qled.

Sorry, 2021 

If the original track is in English, then often that is the only one encoded in Atmos. 

What specifically are you watching on Disney+? The Dolby Atmos audio will usually only be available on the original language audio track.

I believe your Samsung 2021 does not accept Dolby Atmos. I'm almost sure, only in the last 1/2 year have they added it. Sicuramente al 90% dovrai provare la lingua originale.

There might be a difference too in the apps on your TV, some might do Atmos, some might not. On Samsung Disney+ and Atmos has been a problem. Not sure this was solved.

Ok thank you very much... I tried it in the original language and in fact it comes out in Dolby Atmos