Well, there's multiple denoise filters/algorithms that can be used. See eg. https://superuser.com/questions/1547426/using-ffmpeg-to-denoise-reduce-film-grainMXGS-803 - Akiho Yoshizawa is very bad noise :| (look like it was recorded at 6400 or 12800 ISO )
I did denoise but it doesn't help too much
does anyone know the better way to denoise, or have another source videos (i used 56.7 GiB version), please tell me
haiz, denoising took double time than normal encoding but the result is not as expected >_<
if no one has better solution, i have to accept this
As an extreme measures there are AI improvements.