not sure if this has been solved. we had 10x Intel NUC with 11th and 12th gen proc in the field for 4k output which we eventually replaced for Android DSCS9X.
Basically all movie clips are going through Handbrake to get the best output file. Also 4K clips. We have seen that any random 4K clip can stutter because of the used codec. Using Handbrake with Xibo given options, helps a lot.