Try turning off the lens correction module. My guess is that might be the culprit.
As Claes said, have a look at the height and width pixel settings in Export module where you can set what size you want.
I think I found the problem. Darktable is NOT the only software that has the problem. It looks like my goof-up had to do with the camera setting which allows setting an aspect ratio. In this case, it was set to 16:9 which, I think, explains what happened.
However, the reason for shooting raw is that this stuff can be controlled in post processing. I know how to fix it in other programs but NOT DT. This was a hard image to develop and I don’t want to loose any of the stuff that affects appearance.
Hope there is a module that lets me say what dimensions to use for the exported images.
Just got a photo of EOS R captured in 16:9 from the internet. No problems here with aspect ratio, it’s exported as captured without having to set anything at all.
Some people already asked about your export-module settings.
Would you mind to show them? And if nothing else helps, share a raw + xmp?
Oddly that I think darktable doesn’t offer non uniform resizing, neither as a module nor during export. Even if you enter a 4:3 res in export, the photo will be fit into this frame by keeping the aspect ratio.
Following is my export settings where I changed to the size of the raw file. However, the resulting file has a height of 3776.
I’ve been hunting in the User Manual but find no mention of how the change from actual size of raw data to camera set aspect ratio is done. It looks to me like it happens very early in pipeline. For example, the crop module has a setting called “Original Image” for aspect ratio but it uses the 16:9 as original when the raw data is actually 3:2.
Raw sample?
Did the “zero zero” settings produce the same results you are getting now?
YES it did!
Oh, I get it. I misunderstood your problem. I thought, your image was stretched or shrunk, or something like this. 
You just want to remove the 16:9 set in your camera, but I’m afraid thats not possible with DT 
It says 4546 px without cropping the borders, so all the pixels should be there. I suppose this is Libraw that handles this part.
Data is there. But metadata says
and I think there’s no way to tell DT to ignore this. ART / RT do ignore it and open the photo in 3:2. I don’t know if there’s a way to modify the metadata.
I made a sample. The raw has the 16:9 aspect ratio (6720:3776) but raw data is 3:2 (6720:4480). I didn’t do anything to change the neutral settings but did create a jpg with the size set in the Export settings as shown above (6720:4480).
ZIP archive is being uploaded.
AspectRatioSample.7z (41.3 MB)
This is contrary to the whole theory of why raw data is obtained from the camera!
Whole image?
Choose Pass through in Black/White point module. Use crop module to cut off the optical black area.
If I were you I would fill an issue at Github about this and link this thread. Probably Libraw that darktable uses for CR3 files.
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I was able to update the metadata but Darktable (DT) was unable to process the revised file. After getting fatal error I did try to completely remove the former references to this file from the DT library. However, that didn’t help and of course if I had to do that it would be NO help in solving my problem.
The revised raw file follows:
EOSR0189.CR3 (34.4 MB)
darktable uses Exiv2.
$ exiv2 -pv raw-file.CR3
Compare what the difference is between the cropped one and the non cropped. Change the cropped one with exiv2. I have vacation now for a month and will not be near my computer.
The rawprepare module takes care of cropping the whole sensor data to the size exif data is telling.
There are sliders that can override exif settings, by default they are hidden for safety reasons.
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Peter, I’ve been using ExifTool for some time now. I have been able to change the aspect ratio elements in the metadata (Makernotes) successfully (Note: the image file I previously uploaded after changing metadata was NOT completely changed. It’s still flawed). That appears to provide a way to fix the raw file. In that, before investing time and effort to develop. However, it does NOT appear to be any help when it comes to salvaging past work done on developing an image file.
Even though I did nothing to alter the aspect ratio (or size) of the image it looks like something is present in the sidecar file that preserves the aspect ratio in effect when the developing was done.