Olympus E-M1X has a 20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features Dual TruePic VIII processor. On the other hand, Panasonic GH5S has a 10.0MP Four Thirds (17.3 x 13 mm ) sized CMOS sensor and features Venus Engine 10 processor.
Olympus E-M1X's sensor provides 10MP more than Panasonic GH5S'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.
One other difference between these two cameras that is worth mentioning is that Panasonic GH5S'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 moire occurring in certain scenes.
Below you can see the E-M1X and GH5S sensor size comparison.
Olympus E-M1X and Panasonic GH5S have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.