I noticed Apple using a lot of noise reduction on my previous phone, the 8 Plus. Their algorithms seemed to mistake some details, like a cat’s fur, for noise and would apply it’s automatic noise reduction when using the Apple’s camera app. Photos shot with other camera apps in JPEG looked significantly better. Shooting in a RAW format was obviously even better.
I now have the XS Max. Using Apple’s camera app produces much better pictures that the previous sensor, but in lower light, there is a ton of noise reduction added, even with the rear camera. It’s more noticeable with the front camera due to the lower resolution. I don’t personally know if it affects selfies more as I don’t really take selfies.
But needless to say, Apple’s camera app adds noise reduction as it sees fit and it doesn’t always get it right. I am a photographer and noticed this right away with both phones. But as far a a little camera built into a phone, it does a really great job.
If Apple’s noise reduction is mucking up your photos, there are any number of camera apps that shoot in RAW that you can get that will drastically up your mobile photography game. I highly recommend shooting with 645 Pro and using Lightroom for editing. But there are many other options that might be better for you.