Give it more time. If you had enabled analytics reporting it can take time to transfer that data. If it hasn’t completed after an hour force-restart the iPhone and try again. In general, updates can take up to a hour or sometimes longer, depending on your internet connection speed.
Forced restart:
- Press and quickly release the volume up button.
- Press and quickly release the volume down button.
- Press and hold the side button until you see the Apple logo (this might take longer than 10 seconds).

The operative word here is QUICKLY for the first two buttons, then a long hold for the SIDE button; and try it a couple of times, the timing is a little tricky. If done correctly this will always work unless the phone has a hardware problem.