To be compliant with Apple's requirements, those who want to test out iOS 17 will need a device from the iPhone XS series or later. It appears that the outdated A11 Bionic chipset is the bottleneck for the iPhone X and 8 series since the second and third-generation iPhone SE models are still supported.
When we switch to iPadOS 17, we can see that Apple is discontinuing support for its first-generation iPad Pro models and the 2017-released fifth-generation iPad.