Both Sony RX100 IV and Panasonic ZS100 have 20.0 MP resolution sensors but Sony RX100 IV's sensor is 1" (13.2 x 8.8 mm ) and Panasonic ZS100's sensor is 1 (13.2 x 8.8 mm ).
Since Panasonic ZS100'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 Sony RX100 IV.
Below you can see the RX100 IV and ZS100 sensor size comparison.
Sony RX100 IV and Panasonic ZS100 have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.