Panasonic S5 II has a 24.0MP Full frame (35.6 x 23.8 mm ) sized CMOS sensor and features Venus Engine processor. On the other hand, Sony A7S III has a 12.0MP Full frame (35.6 x 23.8 mm ) sized BSI-CMOS sensor and features Bionz XR processor.
Panasonic S5 II's sensor provides 12MP more than Sony A7S III's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Another difference between these two cameras is that Panasonic S5 II'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 S5 Mark II and A7S III sensor size comparison.
Sensor Size and Resolution Comparison image of Panasonic S5 II and Sony A7S III Cameras
Panasonic S5 II and Sony A7S III 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 Sony A7S III has 99% larger pixel area (70.55µm2 vs 35.30µm2) compared to Panasonic S5 II, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.