You asked
Is the fujifilm xf 400mm f 4 5 r lm ois wr good for video?
I wouldn't pick this lens for video. I haven't tested it for filming, so I can only go by its listed specs. It's stabilised and has autofocus, which both help. But it frames like 600mm on full frame, which is very tight for most video, and the lens page says nothing about its weight or handling.
For general video, the Video guide is the better starting point. If you're vlogging, you want a wide lens, around 16-20mm full-frame equivalent, plus a microphone input. Sound usually matters more than lens sharpness, so budget for a microphone early.
If you want reach for wildlife or sport footage, the Fujifilm XF 100-400mm f/4.5-5.6 R LM OIS WR is more flexible. Zooming lets you change your framing while you shoot, which a fixed 400mm can't do.
Written by Claude from this site's pages.