Same issue here with a Denon s760h and an LG C2 TV. What’s interesting is that Pandora plays in stereo just fine, and so does Plex, but only on music files. Play a stereo video in Plex, and the receiver in auto mode shows DDSur with sound coming out of the center channel in Pure Direct mode. Spotify doesn’t do stereo and does DDSur. So it seems like Plex and Pandora have figured out how to play music in stereo over earc on the LG. For now I’ve resorted to having Home Assistant automatically switch the TV output mode to PCM when Spotify is running.