So here is the deal the display profile comes in before the histogram profile. My screen is dark because I set the display profile just for the gamut check to linear rec2020 … I think for darktable the srgb profile will work also because it is unbounded… But to remove this possibiltiy at all you set working, display, and histogram to linear rec 2020… now when you check the overexposure set to full gamut you can see what in the pipeline is gamut clipped… When you select the gamut clipping tool that uses what you have set for softproofing… if its srgb then what it shows is all the gamut that won’t fit in the space…but this is handled by color management and mapped…otherwise if you worry about this then you might as well set it to srgb for everything and that would not make sense… So in a way the gamut warning shows you what will have to be mapped and the overexposure gamut will show you what cannot be accurately mapped to your desired output… I hope that makes sense…
EDIT
So in my mind and I could be wrong but set-up as described above with your softproof profile matching your export or output and your histogram profile matching your working profile and then confirming that your display profile is well behaved by checking what impact changing it to linear rec2020 has… it should be none if it is then that display profile distorts true gamut readings… So then from this diagram A would be rec2020 and B would be SRGB. The gamut warning tool would show the areas shown here as out of gamut and needing to be mapped as well as any area’s beyond that and the overexpose gamut would show you any data clipped outside of the A color space ie rec2020 and so not able to be correctly mapped by the colorspace conversion during export… for sure others here are far more knowledgeable than I but this is how I understand it to work and I think AP has decided to remove the histogram profile in his fork and try to tackle this issue so the display profile cannot be an issue ever…
