The Software Update message box does not go away after the update to 16.1.1 has completed.
Has anyone had an issue with the 16.1.1 upgrade completing and then the Software Update message box will not close?
Tap the ‘ok’ to dismiss the message. If it doesn’t go away, try restarting your iPhone: Restart your iPhone - Apple Support
Or force restart if you can’t restart If your iPhone won't turn on or is frozen - Apple Support