Nikon D3500 has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor and features Expeed 4 processor. On the other hand, Samsung NX30 has a 20.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor and features DRIMeIV processor.
Another difference between these two cameras is that Nikon D3500's sensor lacks anti-alias (Low-Pass) filter. 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 D3500 and NX30 sensor size comparison.
Nikon D3500 and Samsung NX30 have almost the same sensor size so none of them has any significant advantage over other in providing control over depth of field when used with same focal length and aperture.