SMDeGrain

[Selur]

Okay, if the Vapoursynth Preview works fine the issue is probably not with the Vapoursynth script itself.

# Imports
import os
import sys
import vapoursynth as vs
core = vs.get_core()
# Import scripts folder
scriptPath = 'C:/Program Files/Hybrid/64bit/vsscripts'
sys.path.append(os.path.abspath(scriptPath))
# Loading Plugins
core.std.LoadPlugin(path="C:/Program Files/Hybrid/64bit/vsfilters/Support/libmvtools.dll")
core.std.LoadPlugin(path="C:/Program Files/Hybrid/64bit/vsfilters/SourceFilter/LSmashSource/vslsmashsource.dll")
# Import scripts
import nnedi3_resample
import mvsfunc
import havsfunc
# Loading C:\Users\takrayan\Downloads\ExtendedScenes.mkv using LWLibavSource
clip = core.lsmas.LWLibavSource(source="C:/Users/takrayan/DOWNLO~1/EXTEND~1.MKV", format="YUV420P8", cache=0)
# making sure input color matrix is set as 709
clip = core.resize.Point(clip, matrix_in_s="709")
# Making sure input color range is set to TV (limited) range.
clip = core.std.SetFrameProp(clip=clip, prop="_ColorRange", intval=1)
# removing grain using SMDegrain
clip = havsfunc.SMDegrain(input=clip, interlaced=False)
# adjusting output color from: YUV420P8 to YUV420P10 for x265Model (i420)
clip = core.resize.Bicubic(clip=clip, format=vs.YUV420P10)
# Output
clip.set_output()

(yes, script seems fine)
Do you see an error, when you call:

"C:\PROGRA~1\Hybrid\64bit\VAPOUR~1\vspipe.exe" "C:\Users\takrayan\AppData\Local\Temp\encodingTempSynthSkript_08_14_22_7410.vpy" - --y4m | "C:\PROGRA~1\Hybrid\64bit\x265.exe" --input - --output-depth 10 --y4m --profile main10 --qg-size 8 --limit-modes --no-open-gop --radl 2 --lookahead-slices 0 --crf 18.00 --cbqpoffs -2 --crqpoffs -2 --qpfile "C:\Users\takrayan\AppData\Local\Temp\ExtendedScenes_new_08_14_22_7410_02.qp" --psy-rd 2.50 --rdoq-level 2 --psy-rdoq 10.00 --aq-mode 0 --deblock=-1:-1 --limit-sao --range limited --colormatrix bt709 --output "C:\Users\takrayan\AppData\Local\Temp\08_14_22_7410_03.265"

inside a Windows command line prompt?