The LG C1 does not support passthrough for dts audio formats (rtings.com review).
Deselect dts and dts-HD audio in Plex Media Player.
Alternately, try Plex HTPC. Plex HTPC will eventually replace Plex Media Player, which is no longer being developed (last updated May 2020). You may still have to deselect dts in Plex HTPC.
Additional notes:
You could also connect the PC directly to the receiver. That takes any TV restrictions out of the equation.
The Plex PC/Mac client apps play HDR10 media but tonemap it to SDR. If you want HDR output, use the Plex LG app or a streaming box such as an Nvidia Shield, Apple TV, Roku, Amazon FireStick 4K, etc.
Additional info wrt Plex and 4K: [INFO] Plex, 4k, transcoding, and you - aka the rules of 4k
To modify audio formats in Plex Media Player:
- If in Desktop mode, switch to TV mode.
Click on the TV button in upper right part of screen. - Select your username.
- Settings → Audio → Device Type = HDMI.
Audio formats should now be visible. Select which ones you wish to passthrough.
Note 1: You may have to use arrow & enter keys for navigation/selection in some sections of Plex Media Player.
Note 2: Settings/navigation in Plex HTPC is very similar to Plex Media Player.
