VapourSynth IVTC script ... may be the best

ivtc.py

import havsfunc as haf
import functools

input_clip = src
def postprocess(n, f, clip, deinterlaced):
  if f.props['_Combed'] > 0:
     return deinterlaced
  else:
     return clip

matched_clip = core.vivtc.VFM(input_clip, 1)
deinterlaced_clip = haf.QTGMC(matched_clip, TFF=True, FPSDivisor=2)
postprocessed_clip = core.std.FrameEval(matched_clip, functools.partial(postprocess, clip=matched_clip, deinterlaced=deinterlaced_clip), prop_src=matched_clip)
decimated_clip = core.vivtc.VDecimate(postprocessed_clip)

src = decimated_clip