ffmpeg alpha channel?

Question

Video

Good day to all.
I work with ffmpeg. There is a need to convert a video with an alpha channel to .mp4, I know that this format does not support an alpha channel, but I don’t need it, I’m interested in getting this result:
m90.github.io/seeThru/video/kolor.mp4
I found here are the filters:
-vf “[in] format=rgba, split [T1], fifo, lutrgb=r=maxval:g=maxval:b=maxval, [T2] overlay [out]; [T1] fifo, lutrgb=r=minval:g=minval:b=minval [T2]”
But it still didn't work. What am I doing wrong?