How to watch 4k movies properly?

My pc specs are

Cpu: amd ryzen 7600x

ram: DDR5 16gb

GPU: radeon 7800xy

I watch in a TV LG Oled c5 or I use xiaomi tv box s.

I away use direct play because my tv and the tv box can handle all codecs my movies demands.

The problem I am having now is the slow loading when a movie is 50gb+, like interstella and Oppenheimer. Some time did not even load the movie. And if loads when I try to go forwards, the movie is really slow to load that part.

Do you guys has the same problem with heavy movie files?

Neither my tv nor tv box are connected by ethernet cable. The xiaomi with ethernet accepts only 350mbs and the tv less than that, my server are connected by cable