Both Sony A6100 and Panasonic S1 have 24.0 MP resolution sensors but Sony A6100's sensor is APS-C (23.5 x 15.6 mm ) and Panasonic S1's sensor is Full frame (35.6 x 23.8 mm ).
Since Panasonic S1'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 Sony A6100.
One other difference between these two cameras that is worth mentioning is that Panasonic S1'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 A6100 and S1 sensor size comparison.
As seen above, Panasonic S1 has a 2.3x Larger sensor area than Sony A6100. 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.