I figured it out.  My TV firmware Was out of date.  I am now on 5.10.50 version. 
 

rthe arc is now connected through the HDMI ARC connection and getting the Dolby Atmos indicator in the S2 app playing DA movies in Netflix app within Apple TV 4K 

hope this is able to help someone else

It would probably help someone, but you need to say what TV model this is for.

Yes….. you are absolutely correct.  Apologize for that.  My question started off generically and then had a specific fix.  
 

this was for the LG OLED B8 series..

thanks.. good catch

I cannot see a Dolby Atmos indicator anywhere in the S2 app even when I am sure the input signal is Atmos. 
I’ve tried Netflix, the Dolby Atmos demo app in the TV and streaming Tidal within the Sonos app. 
I have brand new WiFi 6 routers, a Sonos Arc speaker and new LG NANO05 TV with HDMI 2.1 and ARC. 

Vizio PX75-G1 (2019) latest firmware. No Atmos signal from the Vudu app or from AppleTV. Anyone have any luck?