Canon M6 has a
24.0MP APS-C (22.3 x 14.9 mm ) sized CMOS sensor and features Digic 7 processor. On the other hand, Canon R7 has a
33.0MP APS-C (22.2 x 14.8 mm ) sized CMOS sensor and features Digic X processor.
Canon R7's sensor provides 9MP more than Canon M6'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 M6 and R7 sensor size comparison.
Canon M6 and Canon R7 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.