Kidney mineralization in stage III senior kitty?

I was wondering if anyone else has experienced this with their kitties?

My cat (16, stage III kidney disease with IBD, arthritis) was at the vet today for litter box straining, and on the xray that was taken the vet said she saw significant kidney mineralization - which isn't something that I knew could be a thing.

She had xrays back in May for constipation, and I remember back then her vet said something about one of her kidneys being cloudy but at the time we were more concerned about her constipation.

In today's xray that mineralization has noticeably gotten worse / progressed. The vet (who isn't her usual vet, her usual vet is out until September) said both kidneys are misshapen and one is enlarged / shows bright white on the xray.

I didn't get a chance to really ask questions, because it was an incidental finding while checking to see why she was straining in both poop & pee stances this morning and we were at the end of the appointment by the time the vet was able to compare xrays from now and May. Roxy's labs have been stable though, her creatinine has been at 3.7 for over a year and her other labs have been normal other than some very slight anemia creeping in recently.

The only thing the vet said was the xrays indicate her kidney disease is likely more advanced/severe than her labwork indicates. I don't really know what that means for Roxy though. I don't know if it's painful for her, if this means anything for where her kidney disease is at or how long I have with her.

She's had some odd things come up recently; I had posted here a week or so ago because she had started experiencing some episodes of abnormal lack of reaction to auditory & visual stimuli. She saw her usual vet last week and what came out of that was it was possible she was having TIAs, or it was possible she was having sundowning moments - but that an MRI would be stressful on her and was more risky / would do more harm than good due to the need for anesthesia and how that affects advanced kidney disease.

Since then I've also noticed her fur is thinning on her left side & part of her spine; she is a medium-longhaired Maine Coon mix and her fur is usually thick & silky smooth. However on the side that she doesn't groom well anymore, her fur is rough/wirey and thin - I can see to her skin when petting her. She does have arthritis that is worse on her back left hind leg, so I attributed the fur thinning to grooming issues due to arthritis.

She also does have some signs that something is bothering her, that or cognitive decline - she's been spending a lot of time under my bed during the day. It's a marked change from a half a year or so ago, she used to spend most of the time with me. She still sleeps with me at night though, in fact she's either looking for comfort or can tell I need comfort because she's sleeping close against my pillow and even against my arm lately.

But going back to the mineralization - I didn't know that can happen to the kidneys themselves, I'm more familiar with mineralization as it relates to kidney stones. Has anyone seen this with their kitty or know more about it? It doesn't feel good that things are progressing even though her labs are stable - I thought if her creatinine has been stable for over a year then her body would be stable / not progressing.