Currently there are 32 native Standard Prime lenses for Sony A6400 and 23 of these lenses are autofocus (AF) type.
Sony A6400 doesn't have a sensor based image stabilization system but 1 of these Standard Prime lenses features optical image stabilization.
Since Sony A6400 has environmental sealings (Weather Sealing), you may like to couple your camera with one of these 11 Standard Prime lenses with Weather Sealings.