so after finding solution why cutscenes from ZZZ lag heavily, it was because that my computer didn't process 4K video fast while Genshin Impact has 1920x1080 resolution of cutscene videos (and Metal Gear Rising too). The only solution is to buy powerful CPU, as most videos put heavy load on CPU (or try disabling unnecessary apps in background, idfk).
i'd recommend compressing usm files but i dont think it would work and may cause game crash.
While i make gameplay videos, i always skip cutscenes (if i replay some of tasks), otherwise, i would enjoy fast slideshow lmfao.

the reason i put spoilers alert is because second image clearly shows major cutscene

it is ending of Raiden bossfight btw

anyways, expect for something fnuuy