Clear Other storage on your iPhone or iPad
If you have iOS 13 or iPadOS 13, your iPhone or iPad storage is full, and the storage is mostly taken up by "Other" storage, update your device to iOS 13.6.1 or iPadOS 13.6.1 or later.
Update your device
An issue in iOS or iPadOS 13 might prevent the system from freeing up storage for you. To fix this issue, update your iPhone or iPad to iOS 13.6.1 or iPadOS 13.6.1.
If you don’t have enough available storage to update wirelessly, update your device to iOS 14.1 or iPadOS 14.1 or later using a computer.