Fujifilm lossy compressed raw still isn't supported after many years [1].

[1] https://github.com/darktable-org/rawspeed/issues/366

And in my experience there has been lots of bugs with Fujifilm raws in darktable:

[2] https://github.com/darktable-org/rawspeed/issues/354

[3] https://github.com/darktable-org/darktable/issues/18073

However, Fujifilm lossless compressed raw actually does a decent job keeping the file sizes down (about 50% to 60% the file size of uncompressed) while maintaining decent write speed during burst shooting.