OK, just a Darktable noob and I have gotten it to correctly export data to JPEG, but there is no EXIF data in JPEG-2000 or AVIF (which I'd rather use to get 12-bit color and wide gamut). Is there some setting somewhere to enable this?
You might want to check https://github.com/darktable-org/darktable/issues to see if it is known issue. If it is not listed you can open a new issue.