You asked
Is the sony fe 100 400mm f 4 5 gm oss good for portraits?
Honestly, I wouldn't pick the Sony FE 100-400mm f/4.5 GM OSS for portraits. It's built for sport and wildlife, and the 100mm end is the only part of its range that suits people. At that focal length you'll be a long way from your subject, and the 400mm end is far too long for most portrait work. It is stabilised and fast enough for telephoto subjects, so it's a strong sports and wildlife lens, just not a portrait lens.
My rule on Portraits still holds: the lens matters far more than the camera. Look for a prime in a portrait focal length, and check the lens page for the full list of bodies it fits if you already own one.
Written by Claude from this site's pages.