I found this old video from Aurelien useful as a tutorial
Also, this suggestion from @Claes was very useful:
“In darktable, also invoke the rgb levels module. Click the auto button. That will bring up your whites”
Personally, I also moved any modules where I am adjusting the edit after (above) negadoctor in the pipeline so that the sliders don’t operate in the opposite direction to a normal (positive) file