https://www.cnet.com/news/iphone-xr-this-is-what-to-expect-from-the-camera/

That looks like a lot of common ground. Both phones also share the same computational photography pipeline, using the A12 Bionic chip and the image signal processor.

But the big difference is that the XS and XS Max have an additional 12-megapixel f/2.4 camera at the back, which is used for 2x optical zoom. It's also an important part of portrait mode, as that telephoto lens helps create a depth map that determines where your subject is in relation to the background.