Canon 80D has a 24.0MP APS-C (22.5 x 15 mm ) sized CMOS sensor and features DIGIC 6 processor. On the other hand, Canon 4000D has a 18.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 4+ processor. Canon 80D's sensor provides 6MP more than Canon 4000D's sensor, which gives a significant advantage in real life. You can print your images larger or crop more freely.
On the other hand, please keep in mind that Max sensor resolution is not the only determinant of resolving power. Factors such as the optical elements, low pass filter, pixel size and sensor technology also affects the final resolution of the captured image.
Below you can see the 80D and 4000D sensor size comparison.
Canon 80D and Canon 4000D 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.