Both Nikon D3500 and Nikon D7100 have APS-C sized 24.0 MP resolution sensors so sensor size and resolution is not a differentiator between these two cameras.
Another similarity between these two cameras is that both Nikon D7100 and Nikon D3500 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 D3500 and D7100 sensor size comparison.
Sensor Size and Resolution Comparison image of Nikon D3500 and Nikon D7100 Cameras
Nikon D3500 and Nikon D7100 have the same sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.
Sensor size sets the circle of confusion, so it drives how much depth of field each
of these bodies gives you at a given aperture. You can calculate it exactly for the
Nikon D3500
or the
Nikon D7100 ,
including hyperfocal distance.
