Apple periodically updates the list of devices that are compatible with iOS, removing older models and reducing the number of devices the company has to support with the software. For example, with iOS 10’s release, Apple left the original iPad and the iPhone 4S in the cold while still allowing those using the A6 SoC and later versions to be updated.
According to a list from iPhoneSoft, reportedly sourced from a senior engineer at Apple who works on one of the teams associated with iOS 13, the newest version will not work with the iPhone 5s, iPhone 6, iPhone 6 Plus, nor the iPhone SE.
