I was going to suggest you do a search because a few others have commented same for both Xr and Xs but I see you have already replied in another discussion, so I will forget that.
This is just my view and may be incorrect, but I haven't seen any really change to the quality of images on my X, and I've had the device from release so that covers iOS11 and now 12, so I don't believe it's entirely software related. I believe with the release of the new iPhones came new hardware and a different way to capture the image (the merging of more shots) that might be giving some users cause for concern under certain conditions.
Have a read through this blog for a more detailed comparison on how Apple are now doing the imaging a little differently.
https://blog.halide.cam/iphone-xs-why-its-a-whole-new-camera-ddf9780d714c
I'm not sure which options are available for the Xr under the camera setting, but you could experiment by turning off Smart HDR/Auto HDR or any other "processed" option and see what the differences are with respect to sharpness and pixelation, also using a different camera app may alter how things are ultimately processed and displayed.
On my X with Auto HDR you can opt to keep the "normal" image as well, and under certain conditions you can end up preferring one to the other, likewise using another app can result in same, so in the end you just have to find what works best under which conditions.
The blog does say that Apple's new way is in early days, and as software gets better it should improve because it's taking better advantage of the hardware, time will tell.
Hope some of the above is of interest.