Thanks everyone, I have the answers I need : the file is demosaiced so that is that.
I can open it in a fashion with darktable… I’m sure that will be fixed in a later build. I’m using the ones kindly provided on this thread current OSX Build - #379 by ricochet
I’ll use the dxo dng file for denoising if I find that darktable has trouble with very high iso files. At least I can use the color calibration module as I prefer the color rendering on darktable.
Cheers,
Nicolas