Sharpness centrally is outstanding from f/1.8 right through to f/8 and excellent ... CA (Chromatic Aberration) is measured with any in-camera corrections switched off, as far as we can know ...
Central sharpness is outstanding from f/2.8 right through ... common with some other Nikon Z optics, so it seems to be a design choice. It can of course be handled in camera or in software ...