Not sure this is the right subreddit, but here goes.
When I'm watching a YouTube video that's 4k and HDR with the built-in chromecast, my TV lags slightly. And by this I don't mean buffering, it is simply stuttering and not smooth. 1080p and HDR works smoothly. Any idea of how to fix it, or is the built-in chromecast simply incapable of being stutter-free?
The YouTube app does not stutter with 4k, however the app doesn't work with HDR as far as I know.
I get the same with my Sony TV. It used to be terrible before Nougat come along but the update smoothed it out some.
Try limiting background processes, see if that helps.