The settings on the Denon is easy, it's all on the video setting screen. It is the 4K TV's menu that may have some deep layers to go through in order to find all the things you need to do, that's the case with my Sony, it may be quite different for LG.
Once you have the settings figured out, please turn the TV and AVR off and then pull the plug on both and wait a minute (just to be 200% sure) before plugging them back on. As I mentioned, the switching to/from TV audio may take a few seconds. Good luck!
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