The iPhone XR can take some quality portrait mode photos with its single camera, but there's a catch: for now, its reliance on software-based object detection limits it to photos of people. You might have more flexibility before long. The developers of the camera app Halide have found enough available depth data to snap portrait shots of non-human objects, starting with pets. The depth map is crude and could lead to more "temperamental" photography than with the iPhone XS' dual cameras, particularly in situations where there's not enough difference between the foreground and background. However, it's at least "usable."
It's not certain when you'll have the option of capturing these portraits with Halide, but this should open the door to taking portraits with other apps as well. It's also a reminder that Apple's own approach isn't necessarily set in stone and could change through software, even if it's unlikely to have the XS' sheer flexibility any time soon.