You asked
Is the canon rf 800mm f 11 is stm good for video?
I don't have a verdict on this lens for video. The lens page lists it as stabilised with autofocus, but it doesn't say how it performs when filming. It's a very long, slow telephoto, so it's mainly a lens for distant subjects in stills, and I wouldn't pick it as a video lens without more information.
If you're shooting video, the video guide covers what matters most: audio, a light setup you can hold steady, and a lens that suits the shot. The lens page also lists which Canon bodies it fits, from full frame to APS-C.
Written by Claude from this site's pages.