After making a severe perspective change (in darktable), I was unable to crop/eliminate all of the black border without compromising the final image material.
I found that retouch (also spot removal) was unable to replace the black sky area … it simply does not work but I was able to make the repair through an exported tiff version.
Not a big deal but interesting!
Happened to me once or twice. Corrected it in Gimp after exporting the final image in darktable as a PNG.
Wonder if it’s possible to change that behavior in darktable without messing up the pixelpipe