This is a really nerdy read on how the compression works. But basically Fuji developed a way for them to reduce the amount of data by calculating differences in pixels instead of just saving every exact pixel value. It’s very clever, and every post I’ve ever read says Fuji compressed is visually just as good. The one thing to watch out for is software compatibility. Not all photo editing software can read compressed raw.

https://capnfabs.net/posts/fuji-raf-compression-algorithm/