Hi,
Issue: the exported file (f32-bit float REC2020) is a lot different from what I was seeing while editing:
The image at left is the edited tiff, as I perceived it while editing. At right, the exported tiff. Shouldn’t they be the same? The main difference lies in the sky: the reds and blue are washed out.
Have you opened the edited tif in the darkroom view or tried viewing it in another, color-managed application?
Yes, and it’s the same as show at right, above (washed out)
I first noticed it when I opened the first version of the exported file in Gimp.
After that, I deleted DT .config folder, reopened the edit file (the one at left above) and exported it again. Same issue. It’s the one shown at right above
It seems like some of the tools weren’t applied to the exported file, but that’s only a guess.
Did GIMP prompt you to keep the REC2020 profile or switch to the sRGB?
No, but the last days I’ve been doing basically the same edits on other pictures, then opening the exported tiffs on Gimp, and it never asks that, but the exported tiffs are the same as they showed before exporting
In the export dialog in darktable, it says the color profile is REC2020?
Please export the image with a resolution of something tiny like 10x10 pixels, then zip it and then upload it here. The zipping is because I don’t trust the forum to leave all metadata untouched.
we actually fixed that you grumpy old man 
Maybe you did, maybe you didn’t. No need to risk anything if the solution is as simple as putting the file into a container.
Sorry for the late reply. I don’t see anything suspicious in that file. The right color profile is embedded and darktable recognizes it.