https://arstechnica.com/gadgets/2024/06/these-are-all-the-devices-compatible-with-ios-18-and-ipados-18/

Apple's new iOS 18 and iPadOS 18 updates are mostly good news for users of older Apple devices—with the exception of 2018's sixth-generation iPad, the new updates will run on all the same hardware that can run iOS 17 and iPadOS 17.

For iPhones, that will cover everything from the iPhone XR/XS and newer, including the second-gen iPhone SE; the seventh-gen iPad and newer; the third-gen iPad Air and newer; the fifth-gen iPad mini and newer; all 11-inch iPad Pros; and the third-gen 12.9-inch iPad Pro and later. Here are the full support lists: