Couple of things. First, Dolby Digital 5.1 is not ‘better’ than Atmos, as a codec. However, your Beam gen 2, while up it can interpret Atmos, it doesn’t have the upward firing speakers built in, so it interprets the signal into the speakers it has.

Second, Atmos (and Dolby Digital) are codecs. That means the show being watched must send that codec. You’re extremely unlikely to get Atmos out of 90% of the content on your TV, unless you’re watching movies created in the last two years exclusively. Most sports and news programs are either stereo, or at best Dolby Digital. You’d need to see the Atmos sigil on the broadcast before your TV would send the Atmos signal to the Sonos.

Which brings up the third point. Not all TVs (or cable/satellite boxes) have the ability to pass an Atmos signal to the Sonos. While the Sonos is reporting to the CEC system in your TV that it can accept Atmos, that system may not be able to receive and process Atmos, which it wouldn’t be able to pass on to the Sonos.

So all sorts of misunderstandings, and false information you’ve received. 

For us to help you further, we’d need specifics about your LG OLED TV, specifics about what is connected to it (and how), and specifics about what you’re watching as a test case. 

Thank you for the comprehensive reply. I have resolved the issue by resetting the LG TV by switching off the power supply and holding the on/off button for 30 seconds, suggested by LG customer support. I watched Indiana Jones, Dial of Destiny through Apple TV app and the sound showed as Dolby Atmos on the Sonos app. It sounded amazing!