In fact, it seems like it’s quite a widespread problem, and the exact cause is unclear. It’s certainly not a lack of storage space. Some affected users report having tens of gigabytes free. So, if you’re affected by this ‘iPhone storage almost full’ bug, what should you do? Do nothing. Wait it out for a fix from Apple. What you shouldn’t do is start deleting stuff because: I’ve spoken to an Apple support agent contact who tells me that Apple is aware of this bug, there’s nothing that support techs can do about it, and that it’s something that Apple will need to fix as part of the iOS 15.x update.
