Both Canon M5 and Panasonic S5 II have 24.0 MP resolution sensors but Canon M5's sensor is APS-C (22.3 x 14.9 mm ) and Panasonic S5 II's sensor is Full frame (35.6 x 23.8 mm ).
Since Panasonic S5 II'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 Canon M5.
One other difference between these two cameras that is worth mentioning is that Panasonic S5 II'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 M5 and S5 Mark II sensor size comparison.
As seen above, Panasonic S5 II has a 2.5x Larger sensor area than Canon M5. 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.