Both Canon T8i and Nikon D5200 have 24.0 MP resolution sensors but Canon T8i's sensor is APS-C (22.3 x 14.9 mm ) and Nikon D5200's sensor is APS-C (23.5 x 15.6 mm ).
Since Nikon D5200'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 Canon T8i.
Below you can see the T8i and D5200 sensor size comparison.
As seen above, Nikon D5200 has a 1.1x Larger sensor area than Canon T8i. 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.