That’s an interesting result.
When I inspected my pic in darktable I had negative values all over.
But digging more into it (Darktable 3.4):
The RGB values the color picker shows depend on the setting of histogram and softproof profile. If both profiles point to srgb I get negative values…
If I change the histogram profile to lets say linear ProPhoto the lowest RGB value I can find is zero…
Does that makes sense?