Both Olympus E-M10 IV and Samsung NX200 have 20.0 MP resolution sensors but Olympus E-M10 IV's sensor is Four Thirds (17.4 x 13 mm ) and Samsung NX200's sensor is APS-C (23.5 x 15.7 mm ).
Since Samsung NX200's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Olympus E-M10 IV.
Below you can see the E-M10 IV and NX200 sensor size comparison.
As seen above, Samsung NX200 has a 1.6x Larger sensor area than Olympus E-M10 IV. 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.