So to update how much data is required

benedict45 Said:

"So to update how much data is required"

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Just Keep Unused Space at 40%:

Keep at least 40% free space on your iPhone at all times. That would do just fine, being that you would have to worry about issues like this. If you were to fill it to the top(0% free space), then you may have to reformat your iPhone to factory settings, and then set it up as a new device.

Here is what showed on my iPhone 13 Pro. However understand that you will generally need more than twice that to allow the update to be unpacked from the file.