APPLE INSIDER
Apple’s latest iOS 13.6 and iPadOS 13.6 releases include a new Settings toggle that allows the device to automatically download future software updates. Here is how to turn automatic downloads of iOS updates on or off.

Apple has long allowed iPhone and iPad users to automatically install software updates overnight after they were manually downloaded. The new feature in iOS 13.6 and iPadOS 13.6 further automates the process by downloading new operating system versions without user intervention. That said, the system still alerts users before installing the software.
Source: APPLE INSIDER