Canon R7 has a
33.0MP APS-C (22.2 x 14.8 mm ) sized CMOS sensor and features Digic X processor. On the other hand, Canon 550D has a
18.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 4 processor.
Canon R7's sensor provides 15MP more than Canon 550D'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 R7 and 550D sensor size comparison.
Canon R7 and Canon 550D 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.