Black/white:
ffmpeg -i VID_20210131_202207090.mp4 -vf format=gray VID_20210131_202207090-gray.mp4
Blur:
ffmpeg -i VID_20210131_202207090-gray.mp4 -filter_complex "[0:v]boxblur=luma_radius=10:chroma_radius=10:luma_power=1[blurred]" -map "[blurred]" VID_20210131_202207090-gray-blur.mp4