Is there anything I can do about this extremely vague block of data that’s taking up 30% of my phone’s storage? Mind you, this isn’t the operating system itself, as that’s listed as its own category.
EDIT: I tried (a) backing up to my computer, factory resetting, then restoring from backup and (b) setting the date years in the future. Neither worked, in fact (a) actually increased my system data to 34 GB! What DID end up working was updating my iOS from 18 to 26, which I had to do from my computer via iTunes since my phone was full. Apparently major system updates reset system data
YMMV, but this problem went away for me when I disabled syncing to my MacBook via WiFi. My guess is that it was caching backup images but never successfully copying and removing them.