Both Nikon Z50 and Nikon 1 J5 have 21.0 MP resolution sensors but Nikon Z50's sensor is APS-C (23.5 x 15.7 mm ) and Nikon 1 J5's sensor is 1' (13.2 x 8.8 mm ).
Since Nikon Z50'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 Nikon 1 J5.
Another similarity between these two cameras is that both Nikon 1 J5 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 moiré occurring in certain scenes.
Below you can see the Z50 and J5 sensor size comparison.
As seen above, Nikon Z50 has a 3.2x Larger sensor area than Nikon 1 J5. 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.