How to use Avisynth and load script directly into VEAI and output still images.

[Selur]

I tried this settings what am I doing wrong?

From your description before I would have used:
a. the ColorMatrix filter convert the color matrix
b. the Levels filter to adjust the gamma
c. configured ProRes to reflect the new color matrix in it's VUI settings.

Looking at your screenshots, I don't know why you are doing what you are doing.

• You tell Hybrid the source is TV Range and bt470bg should be used as color matrix. -> Okay.
  
• You use FFmpeg color adjustments to change the gamma. -> No clue why?
  I would not start mixing FFmpeg and Avisynth/Vapoursynth processing unless I'm totally sure that it makes sense and does what I indent it to do.
  
• You change the color space in a custom addition in an Avisynth script, but you are not letting Hybrid know what you did. (This seems strange, especially since bt470bg and rec601 are basically the same so I would have suspected that this would not change much.)
  

Assuming your ProRes settings reflect the color matrix change, I would have suspected that the only thing that changed it the color sampling and the gamma, but no other color change.

I have no clue what the logic is behind what you are doing, but I dare not to doubt you, since you directly used the custom part to add custom additions to the generated Avisynth script. I assume you verified your changed using the script view and Avisynth preview.
So assuming the script and the script output look the way you intended, you configured the ProRes encoding properly Hybrid should abide by those settings.
Without knowing any real detail I have no clue what could have gone wrong.

Cu Selur