Olympus E-M1 III has a 20.0MP Four Thirds (17.4 x 13 mm ) sized CMOS sensor and features TruePic IX processor. On the other hand, Leica SL2-S has a 24.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Maestro III processor.
Another similarity between these two cameras is that both Leica SL2-S and Olympus E-M1 III 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 E-M1 III and SL2-S sensor size comparison.
As seen above, Leica SL2-S has a 3.8x Larger sensor area than Olympus E-M1 III. 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.