I realize this is old but what you want to do is go to your tv’s sound menu and ensure e-ARC is enabled as well as having “passthrough” for the digital audio type. I haven’t had an LG since the first gen OLEDs but did run into this issue with my new Samsung QN95, however my Denon x4300h doesn’t support e-ARC so I use a Thena Audio sHARC converter which accepts the tv’s e-ARC output, some magic happens and than I run the converters output into one of the inputs on my Denon. I’ve been using it for about 6 months and it’s flawlessly passed lossless Atmos. Anyway, when I first set it up I noticed that depending on my source it wouldn’t always pass multichannel audio regardless if it’s 5.1 DD+ or 7.2.4 Dolby True HD Atmos. I had my “digital audio output type” in auto and that’s been empirically proven to cause issues with specific content which results in your tv passing a PCM 2.0 signal with no LFE channel. It’s an issue many HDMI 2.1 tv’s had when first released. You may also want to go to speaker setup>manual setup>speaker config and ensure all your speakers are set to small and your SW is set 1 or 2sp. Additionally check the “Two channel speaker settings” in the same menu and see if they’re set as large with subwoofer as “None”, if you have your AVR in “auto” mode when it receives a PCM 2.0 signal it will recognize a two channel stream and in “auto” it will change the speaker config to what your two channel settings are. Additionally ensure you’re not in direct or pure direct modes.
