Nikon Z50 has a 21.0MP APS-C (23.5 x 15.7 mm ) sized BSI-CMOS sensor and features Expeed 6 processor. On the other hand, Fujifilm X-S10 has a 26.0MP APS-C (23.5 x 15.6 mm ) sized BSI-CMOS sensor and features X-Processor 4 processor.
Fujifilm X-S10's sensor provides 5MP more than Nikon Z50'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-S10 and Nikon Z50 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 moire occurring in certain scenes.
Below you can see the Z50 and X-S10 sensor size comparison.
Nikon Z50 and Fujifilm X-S10 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.