Both Canon R8 and Canon R10 have 24.0 MP resolution sensors but Canon R8's sensor is Full frame (36 x 24 mm ) and Canon R10's sensor is APS-C (22.2 x 14.8 mm ).
Since Canon R8's has a larger sensor area with the same resolution, this means that it also has a larger pixel area hence better light collecting capacity for a given aperture compared to Canon R10.
Below you can see the R8 and R10 sensor size comparison.
As seen above, Canon R8 has a 2.6x Larger sensor area than Canon R10. Larger sensors give photographer more control on the depth of field and blurry background compared to smaller sensor when shot in same focal length and aperture.