Both Nikon D850 and Nikon Z7 have 46.0 MP resolution sensors but Nikon D850's sensor is Full frame (35.9 x 23.9 mm ) and Nikon Z7's sensor is Full frame (35.9 x 23.9 mm ).
Since Nikon Z7's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Nikon D850.
Another difference between these two cameras is that Nikon D850's sensor lacks anti-alias (Low-Pass) filter. 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 D850 and Z7 sensor size comparison.
Nikon D850 and Nikon Z7 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
DxOMark Sensor Scores
Both Nikon D850 and Nikon Z7 sensors have been tested by DxoMark. DxoMark scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Of the two cameras that we are comparing, D850 has scored 100, 1 points higher than Z7.