You asked
Is the nikon z 24 120mm f 4 s good for portraits?
It's a decent walk-around option for portraits, but it isn't a portrait lens. On full frame, its 70-120mm end is in the flattering range, so you can stand back and frame people comfortably. The f/4 maximum aperture gives less background blur than the lenses I'd reach for, though, so faces won't separate from busy backgrounds as much.
If portraits are the main job, I'd look first at an 85mm f/1.8 for the classic look, or a 50mm f/1.8 if you want one cheap lens for everyone. For more distance and softer backgrounds outdoors, a 70-200mm f/2.8 is the one to aim for. The 24-120mm is a sensible all-rounder if you want one zoom for everything, and it fits full frame bodies like the Nikon Z6 II, Nikon Z7 II and Nikon Z8.
Written by Claude from this site's pages.