You asked
What cameras fit the fujifilm xf 400mm f 4 5 r lm ois wr?
Every camera on the lens page is a Fujifilm X-mount APS-C body, so this lens fits the whole APS-C X system, from the X-E1 and X-Pro1 up to the X-T30 III. The full list is on the Fujifilm XF 400mm f/4.5 R LM OIS WR page.
For wildlife, I'd pair it with a body you can hold steady for a long time. The Fujifilm X-H2 and Fujifilm X-H2S are my first picks. If you want to spend less, the Fujifilm X-T3 still gives you the same 600mm-equivalent reach.
If you're not sure how much reach you need, the wildlife and sport guide is a good place to start.
Written by Claude from this site's pages.