Sigma Quattro has a
29.0MP APS-C (23.5 x 15.6 mm ) sized CMOS (Foveon X3) sensor and features Dual TRUE III processor. On the other hand, Fujifilm X-H2S has a
26.0MP APS-C (23.5 x 15.6 mm ) sized Stacked BSI X-Trans sensor and features X-Processor 5 processor.
Another similarity between these two cameras is that both Fujifilm X-H2S and Sigma Quattro sensors lack anti-alias (Low-Pass) filters. 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 Quattro and X-H2S sensor size comparison.
Sigma Quattro and Fujifilm X-H2S 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 Sigma Quattro has 32% larger pixel area compared to Fujifilm X-H2S, it has potential to collect more light on pixel level hence have less noise in low light / High ISO images.