Canon R6 has a 20.0MP Full frame (36 x 24 mm ) sized CMOS sensor and features Digic X processor. On the other hand, Canon R has a 30.0MP Full frame (36 x 24 mm ) sized CMOS sensor .
Canon R's sensor provides 10MP more than Canon R6'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.
Another difference between these two cameras is that Canon R6'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 moire occurring in certain scenes.
Below you can see the R6 and EOS R sensor size comparison.
Canon R6 and Canon R have sensor sizes so they will provide same level of control over the depth of field when used with same focal length and aperture.