Nikon Z8 has a
46.0MP Full frame (35.9 x 23.9 mm ) sized Stacked CMOS sensor and features Expeed 7 processor. On the other hand, Leica M-Monochrom has a
18.0MP Full frame (36 x 24 mm ) sized Monochrome CCD sensor .
Nikon Z8's sensor provides 28MP more than Leica M-Monochrom's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the Z8 and M-Monochrom sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon Z8 and Leica M-Monochrom Cameras
Nikon Z8 and Leica M-Monochrom have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon Z8
or the
Leica M-Monochrom ,
including hyperfocal distance.