I take a lot of pictures with my iPhone. I’m currently using a 13. All of my phones have taken really great pictures. I’ve had many of them enlarged (ordered online at Walmart Photo) and framed. I’ve had blankets made for the grandmas with pictures of the kids on them. But within the last year or so, every time I’ve tried to enlarge one of my photos, I’m told that the quality of the picture won’t be good (I can’t remember the exact wording used). The same thing happened when I tried to create a photo blanket for a friend. The last time I had some of the pictures made into 4x6 prints, they looked pretty crummy. Not crisp, not very clear - nothing like they have in the past. All of the pictures look beautiful when viewing them on my phone.
It might be that the storage on the phone was getting full, and the phone automatically reduced resolution. If that’s the case, then clear up space and set the settings to the desired resolution.
I had to go to my phone settings and change it. then I had to find the setting to “don’t reset camera settings” which confusingly was also what I wanted - otherwise each time I opened Camera, it reset to HEIC. BTW, HEIC is how you get those little videos where you capture a second of action during the photo. I wonder if that was messing up the photo printing? (Yes, nobody else does HEIC).