Update to iOS 14.0.1.
I have iPhone 4S iOS 9.3.6, iPhone 6 iOS 12.4.8, iPhone SE iOS 14.0.1, iPhone 8 iOS 14.0.1 and an iPad Pro iPadOS 14.0.1. Prior to that I had iPhone 3GS, which I have stopped using because it is carrier locked.
I have been updating all these devices whenever a new iOS are released. I have never encountered any issue whatsoever after any update because I have never downloaded anything over the internet directly. Always used apps from App Store only.
Though iOS is not released for many of the above devices, but I do not find any issue in its functionality.