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 R5 has a 45.0MP Full frame
(36 x 24 mm ) sized CMOS sensor and features Digic X processor.
Canon R5's sensor provides 25MP 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.
Below you can see the R6 and R5 sensor size comparison.
Canon R6 and Canon R5 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 R6 has 122% larger pixel area compared to Canon R5, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.
DxOMark Sensor Scores
DxOMark is a benchmark that scientifically assesses image quality of camera sensors. It scores camera sensors for color depth (DXO Portrait), dynamic range (DXO Landscape) and low-light sensitivity (DXO Sports), and also gives them an overall score. Canon R6 and Canon R5 sensors have been tested by DxO and the results show that R5 has a better overall score of 95, 5 points higher compared to R6's score of 90.