XS and XS Max have two cameras on the back (two lenses, two sensors, one telephoto, one wide angle) XR only has one (wide angle)

All three do Portrait mode, although XR uses its wide angle lens and computational photography for that, whereas both XSs use their two lenses (and the subtle shift between the two) with computational photography to make a bigger resolution depth map

I have a XS Max, but I'd say the XR is excellent (camera wise) and good enough for almost everyone. Let that not be your deciding factor

It’s messy right now. -S still means an improved version of a previous form factor (X->XS, just like 6-6S a few years ago.) X- seems to mean a curved corner screen and no home buttons (X/XS, XS Max, XR.) Max And Plus both mean a larger version of another phone (XS/XS Max, but it’s confusing because the XR also has a bigger screen.)

I agree it’s not worth thinking about unless you’re really into Apple news.