DNG has nothing to do with free software, it's an Adobe format similar to PDF. It is an open standard, but it is covered by patents and it comes with a no-cost patent license (except that it's less open than PDF because it doesn't define the interpretation for Adobe-specific tags (which ACR/Lightroom uses), not that that matters for raw file in any way).

Of course that even Adobe DNG converter can do what the GP asked for (I just tried it[1]), not that I would recommend it for Fuji files. And not that it matters anyway, since the whole point is producing DNG files directly, not converting them.

Edit: on my Fuji X-T5 files, using mosaiced data with lossless JPEG-XL compression (supported by MacOS 14+, iOS 17+, and the latest Lightroom/ACR):

    edengate:1$ ls -l
    total 163664
    -rwx------@ 1 aram  staff  40894672 Apr  4 15:25 DSCF1483.RAF
    -rw-r--r--@ 1 aram  staff  42894224 Apr  7 16:51 DSCF1483.dng