Fujifilm X-T30 has a 26.0MP APS-C (23.5 x 15.6 mm ) sized BSI-CMOS sensor and features X-Processor 4 processor. On the other hand, Pentax K-S2 has a 20.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features PRIME MII processor.
Fujifilm X-T30's sensor provides 6MP more than Pentax K-S2'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 Pentax K-S2 and Fujifilm X-T30 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 X-T30 and K-S2 sensor size comparison.
Fujifilm X-T30 and Pentax K-S2 have 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 Pentax K-S2 has 30% larger pixel area (18.37µm2 vs 14.12µm2) compared to Fujifilm X-T30, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.