4:3 vs 16:9

AFAIK iPhones always shoot photos at 4:3 whole sensor and then just crop that to 16:9 for viewing (while preserving the original 4:3 version). Maybe the cropping process does what you are seeing? So try to compare 16:9 to the original 4:3 version.

I did a quick test with .heic and it seems that iPadOS 17.3.1 uses the same ~1:26 compression for the 16:9 version as for the original 4:3. But re-saving as lossy .heic introduces some generation loss no matter what.

iPhone SE 2022 does not support ProRaw so that option is not possible. But if you want to bypass quality loss as much as possible when cropping .heic, you could do the cropping with some 3rd party app like Lightroom or Photoshop. Then you could also fine-tune where the 16:9 crop takes place vertically.

Just a hunch: It might also be a setting for the Display. The cropped version is having a different distribution of colours from the the original, so any display setting might balance the colours in the cropped version different from the original.

• Is the settings > Photos > Full HDR enabled?
• or the setting "Display and Brightness > True Tone"
• or the setting "Display and Brightness > Night Shift

Try to disable any setting that might change the contrast or color before you compare the cropped version to the original, or compare them side-by-side on a computer.