A:Answer I believe that it would be your LG OLED that would pass the Dolby Atmos information to the soundbar via HDMI eARC. (which is going to be HDMI #2 on your LG OLED).
So your other 3 HDMI connections on your LG TV, such as blu-ray players, gaming consoles, cable boxes, and the Dolby Atmos will be passed to the soundbar via HDMI eARC. You basically have to use HDMI eARC instead of Digital Line-In, RCA or Optical in order to get Dolby Atmos.