Use Simplink on HDMI cable from ST300 to HDMI 3. You can set up all connections in the LG Device Manager (smart menu).
New LG OLED C7 with HDMI ArC connected to Marantz AVR about 5 years old. AVR can handle DD+/TrueHD but not Atmos. Marantz is hub. TV Sound set to HDMI ArC with Simplink on and digital sound to auto. On AVR HDMI control is on. AVR recognizes DD+ signal from TV l, and all I get is clicky staticy noise. No audio from content. If I am just viewing Netflix landing page with stereo I get audio. If I change TV audio to PCM output l, I get stereo audio but can’t get DD+/5.1 Audio when watching the Crown for example. Just replaced HDMI cables thinking that could be issue and no luck. Reset TV to factory settings and no luck.