Ricoh GR III has a
24.0MP APS-C (23.5 x 15.6 mm ) sized CMOS sensor . On the other hand, Sony RX100 VA has a
20.0MP 1″ (13.2 x 8.8 mm ) sized BSI-CMOS sensor and features Bionz X processor.
Another difference between these two cameras is that Ricoh GR III'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 moiré occurring in certain scenes.
Below you can see the GR III and RX100 VA sensor size comparison.
As seen above, Ricoh GR III has a 3.2x Larger sensor area than Sony RX100 VA. 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.