For dcraw-rcd, first I opened the raw file with PhotoFlow, told it to use the default dcraw matrix and to output the image still in the camera profile. Then I opened the PhotoFlow output in GIMP-CCE and saved the embedded camera input profile to disk (which GIMP makes easy to do, though you could also use various command line utilities).
Then I processed the raw file with dcraw-rcd, using these parameters:
dcraw-rcd -v -w -q 4 -4 -T -o 0 -H 0 rawfile.ext
which uses the raw file white balance and saves the image as “raw color”. Then I opened the dcraw output tiff with GIMP-CCE and assigned the profile that was saved to disk from the version of the interpolated raw file output by PhotoFlow.
Well, that’s round-about for dcraw-rcd, but it avoids having dcraw do any color management.
In RawTherapee I used the neutral profile as already specified by @heckflosse , then set the working space profile to Rec.2020 (not sure if that matters), and output in RT’s Rec.2020 color space, then opened the RT version with GIMP-CCE, promoted both the RT and the dcraw-rcd versions to 32f, and pulled them both into the same layer stack.
That’s probably way too much detail