Here I found collection of .cube files for doing REC2020 TO rec709.

I extracted one .cube file and run this ffmpeg command (at 1.4 fps on Termux)

ffmpeg -i storage/downloads/iPhone11_4K-recorder_59.940HDR10.mov -vf lut3d=file=REC2020PQto709v1.cube:interp=tetrahedral,scale=1280:-2  ~/1.mp4

and it sort of worked, while I think mpv/libplacebo did better job on my desktop. But even just in mpv I had tons of dropped frames, and decoding in cingg without any tonemapping was at may be 9 fps max, out of 60.

Ow :(

For some reason just throwing F_tonemap to timeline resulted in extremely dark image no matter the settings. I pushed it up by brightness/contrast native plugin but I do not think you supposed to do that?

sw tonemapper was added to ffmpeg in 2017