Sony A7 IV has a
33.0MP Full frame (35.8 x 23.8 mm ) sized BSI-CMOS sensor and features Bionz XR processor. On the other hand, Nikon D810A has a
36.0MP Full frame (35.9 x 24 mm ) sized CMOS sensor and features EXPEED 4 processor.
Another difference between these two cameras is that Sony A7 IV'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 moiré occurring in certain scenes.
Below you can see the A7 IV and D810A sensor size comparison.
Sony A7 IV and Nikon D810A 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.