Sony A7R III has a 42.0MP Full frame (35.9 x 24 mm ) sized BSI-CMOS sensor and features Bionz X processor. On the other hand, Nikon D850 has a 46.0MP Full frame (35.9 x 23.9 mm ) sized BSI-CMOS sensor and features Expeed 5 processor.
Another similarity between these two cameras is that both Nikon D850 and Sony A7R III sensors lack anti-alias (Low-Pass) filters. Removing anti-alias filter increases the sharpness and level of detail but at the same time, it increases the chance of moire occurring in certain scenes.
Below you can see the A7R III and D850 sensor size comparison.
Sony A7R III and Nikon D850 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.