Panasonic G85 has a
16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor . On the other hand, Panasonic G100 has a
20.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor .
Another difference between these two cameras is that Panasonic G85'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 G85 and G100 sensor size comparison.
Panasonic G85 and Panasonic G100 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture. On the other hand, since Panasonic G85 has 27% larger pixel area compared to Panasonic G100, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.