darktable-org
multi_os - ufraw-batch no longer supported
ufraw-batch is no longer available in distributions and appears to no longer be supported. dcraw is still available and appears to still be supported, so the dcraw should be used to extract the embedded thumbnail.
Perhaps a switch to dcraw_emu is even better as it is part of libraw and actively developed. (The last dcraw version is from 2018)
But as dcraw_emu is an example program, Debian doesn't install it to
/usr/bin, but to /usr/lib/libraw instead, meaning it can't be found
the usual way.
Learned something new, thanks. dcraw_emu doesn't support extracting the embedded preview image, however simple_dcraw does with the -e argument. However, simple_dcraw doesn't appear to support many of the newer cameras (Nikon Z, Canon EOS R). Maybe I'll look at how RPD extracts the embedded preview and see if I can get an idea from there.
It turns out you can use exiv2 to extract preview thumbnails. Tried it on a CR3 file and it worked. You can use the command exiv2 -e p ex <image> to pull all of the previews. The first appears to be a small one perhaps for the camera back screen and the second is a full size one.
Btw. I think this is a duplicate of issue https://github.com/darktable-org/lua-scripts/issues/380?
It appears that I didn't do a very good job of looking back. :(