Yours answer seems to indicate that the channel mixer is an elementary and simple tool, easy to master. But that turns out not to be the case. Normally I enjoy the down-to-earth-how-to-use videos from Bruce Williams. I just watched episode 46 of understanding Darktable “The channel mixer”. Bruce Williams spends 21 minutes showing the audience that the channel mixer is somewhat of a mystery (if not used to convert photos to BW).
It’s a smart trick to use the channel mixer with destination grey and blend mode lightness to darken/lighten specific colors.
I have been looking for tutorials explaining how to use the channel mixer in an easy controllable way to fine tune photos but without success. Do you know some good tutorials?