Both Olympus TG-3 and Panasonic GX85 have 16.0 MP resolution sensors but Olympus TG-3's sensor is (1/2. ) and Panasonic GX85's sensor is Four Thirds (17.3 x 13 mm ).
Since Panasonic GX85'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 Olympus TG-3.
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 moiré occurring in certain scenes.
Below you can see the TG-3 and GX85 sensor size comparison.
As seen above, Panasonic GX85 has a infx Larger sensor area than Olympus TG-3. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.