The iPhone and the Pixel both have 12mp main cameras but the S20 Ultra has a monster 108mp camera.
Samsung Galaxy S20 Ultra Camera
Rear cameras: wide-angle 108-megapixel (79-degree) lens, telephoto 48-megapixel (24-degree) lens, ultrawide 12-megapixel (120-degree) lens, DepthVision (ToF)
Google Pixel 4XL Camera
Cameras: Main: 12.2-megapixel, 1.4 μm pixel width, dual pixel phase detection, OIS, ƒ/1.7 aperture, 77-degree field of view. Tele: 16-megapixel, 1.0 μm pixel width, phase detection, OIS, ƒ/2.4 aperture, 52-degree field of view. Video: 1080p @ 30, 60, or 120 fps; 720p @ 240 fps; 4K @ 30 fps; Front Camera: 1080p @ 30 fps.
iPhone 11 Pro Max Camera
12-megapixel “wide” camera with f/1.8 aperture with optical image stabilization (OIS) 12-megapixel “2x telephoto” camera f/2.0 aperture with OIS. 12-megapixel “ultra wide” camera with f/2.4 aperture and 120-degree field of view.