Olympus E-M10 IV has a 20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic VIII processor. On the other hand, Panasonic GX85 has a 16.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine processor.
One other difference between these two cameras that is worth mentioning is that Panasonic GX85's sensor doesn't have an 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 E-M10 IV and GX85 sensor size comparison.
![Olympus E-M10 IV vs Panasonic GX85 Sensor Size Comparison]()
Sensor Size and Resolution Comparison image of Olympus E-M10 IV and Panasonic GX85 Cameras
Olympus E-M10 IV and Panasonic GX85 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.