Nikon D850 has a
46.0MP Full frame (35.9 x 23.9 mm ) sized BSI-CMOS sensor and features Expeed 5 processor. On the other hand, Leica SL2 has a
47.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Maestro III processor.
Another similarity between these two cameras is that both Leica SL2 and Nikon D850 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 moiré occurring in certain scenes.
Below you can see the D850 and SL2 sensor size comparison.
Nikon D850 and Leica SL2 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.