Nikon Z50 has a
21.0MP APS-C (23.5 x 15.7 mm ) sized BSI-CMOS sensor and features Expeed 6 processor. On the other hand, Fujifilm X-A5 has a
24.0MP APS-C (23.5 x 15.7 mm ) sized CMOS sensor .
Another difference between these two cameras is that Nikon Z50'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 moiré occurring in certain scenes.
Below you can see the Z50 and X-A5 sensor size comparison.
Nikon Z50 and Fujifilm X-A5 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. On the other hand, since Nikon Z50 has 16% larger pixel area compared to Fujifilm X-A5, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.