Nikon ZR has a
25.0MP Full frame (35.9 x 23.9 mm ) sized Partially-Stacked CMOS sensor and features Expeed 7 processor. On the other hand, Blackmagic URSA 12K LF has a
98.0MP Full frame (35.64mm x 23.32mm ) sized CMOS sensor .
Blackmagic URSA 12K LF's sensor provides 73MP more than Nikon ZR'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 ZR and URSA Cine 12K LF sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon ZR and Blackmagic URSA 12K LF Cameras
Nikon ZR and Blackmagic URSA 12K LF 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 ZR
or the
Blackmagic URSA 12K LF ,
including hyperfocal distance.