Canon M50 has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 8 processor. On the other hand, Canon 600D has a
18.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 4 processor.
Canon M50's sensor provides 6MP more than Canon 600D'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 M50 and 600D sensor size comparison.
Canon M50 and Canon 600D 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 Canon 600D has 33% larger pixel area (18.54µm2 vs 13.84µm2) compared to Canon M50, it has larger pixel area to collect light hence potential to have less noise in low light / High ISO images.