Hi,
Support of Fuji's compressed raw files has just been added to Rawtherapee 5.0, you can download a build for Windows 64 bits here: https://filebin.net/exoqih33dsopv02q
It's preliminary support, in case you encounter problems, feel free to file a bug report on github (read how to write a useful bug report).
Support of the coming GFX 50S is almost there too.
-Sébastien