Unfortunately, people who have smartphones with older software will soon encounter an unpleasant surprise. As announced by the developer, in an upcoming October update Pokémon Go will end support for Android 5, iOS 10, and iOS 11, as well as iPhone 5s and iPhone 6 devices. Niantic also encourages players to switch to newer devices.
It cannot be denied that such a procedure is understandable despite the disappointment of some fans. Pokémon Go is heavily supported and constantly being expanded. As time went on, the developer had to make a decision that was probably also difficult for them.