Which app are you using on your TV? I've had success direct-playing 4K content with the jellyfin Android TV app. On AppleTV, Infuse works well. Infuse isn't free, but it is worth the money to me.
Wanted to put in a plug for Swiftfin, which plays the formats Infuse wanted to charge me money for, but is free and seems to work well. I use it on the AppleTV mainly.
This is using the native Jellyfin app available for LG's tvOS, so you're at the mercy of the codecs available on the TV. Last time I wanted to watch a movie affected by this, I just plugged in a laptop with an HDMI cable and played it that way.