Leica C-Lux has a 20.0MP (1 ) sized CMOS sensor . On the other hand, Ricoh GR III has a 24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor .
One other difference between these two cameras that is worth mentioning is that Ricoh GR III's sensor doesn't have an 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 C-Lux and GR III sensor size comparison.
As seen above, Ricoh GR III has a 0.0x Larger sensor area than Leica C-Lux. 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.