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, Fujifilm X-H2 has a 40.2MP APS-C (23.5 x 15.6 mm ) sized BSI-CMOS sensor and features X-Processor 5 processor.
Fujifilm X-H2's sensor provides 16.2MP more than Panasonic S5 II'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 similarity between these two cameras is that both Fujifilm X-H2 and Panasonic S5 II sensors lack anti-alias (Low-Pass) filters. 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 X-H2 sensor size comparison.
As seen above, Panasonic S5 II has a 2.3x Larger sensor area than Fujifilm X-H2. 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.