I bought the nikon 85mm f1.2 z some time back but I never had a chance to compare it with the sigma 85mm f1.4 dg dn which I also own.
Below is a series of comparison shots taken handheld. Mainly to check bokeh. Top shot is sigma, bottom shot is nikon.
Other than the first pair which the nikon is obviously better, the difference is smaller than I expected. The BIGGER issues were I forgot to turn of efcs on the Sony and the bokeh WAS HORRIBLE and I had to retake the shots with EFCS off. Also the a7r5 shutter speed were maxed out in some of the shots..