Both Fujifilm X-A3 and Nikon D5300 have 24.0 MP resolution sensors but Fujifilm X-A3's sensor is APS-C (23.5 x 15.7 mm ) and Nikon D5300's sensor is APS-C (23.5 x 15.6 mm ).
Since Fujifilm X-A3'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 D5300.
One other difference between these two cameras that is worth mentioning is that Nikon D5300's sensor doesn't have an 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 moiré occurring in certain scenes.
Below you can see the X-A3 and D5300 sensor size comparison.
Fujifilm X-A3 and Nikon D5300 have almost the same sensor size, so neither of them has any significant advantage over the other in terms of providing control over depth of field when used with the same focal length and aperture.