If you are playing a Dolby Atmos source and the Sonos app is displaying Dolby Atmos, then you are getting Dolby Atmos audio from the Arc.

FYI… Dolby Vision is Dolby’s version of HDR which is related to video not audio.

Thanks for the fast answer. So it is playing dolby atmos.

i dont understand youre last sentence..

The video is playing in 4k ultra hd not HDR. Without the arc it shows dolby digital and dolby atmos in the right upper corner of the tv.

With the arc it shows only dolby digital in the right upper corner of the tv. (Dolby atmos in the app)

Why is that?

HDR is High Dynamic Range, a feature of 4K Ultra HD video.  There are a few types of HDR, such as HDR10, HDR10+, and Dolby Vision.  The TV displaying Dolby Vision has no bearing on whether the Sonos is playing Dolby Atmos.

It seems your question is if there’s something wrong when you notice the TV seems to revert to showing Dolby Digital instead of Dolby Atmos on the screen when it is not playing audio itself but is playing via the Arc.

There is nothing wrong. The TV is passing through the DD+ stream and (trust the Sonos app) Sonos is playing Atmos. All is well.

Thank you all. The sound is amazing!!