Now, I am making an application for a newer model than iPhone8.
However, if I publish the app to the AppStore, users will be able to purchase the app on iPhone7 and so on.
How can I limit which devices users can purchase?
I am creating an app using FaceID.
The app is compatible with iOS 13.1 or higher, but does not work on iPhone7.
Apple expects devs to primarily support iOS version(s) not device(s). Device support is otherwise dictated by required hardware compatibilities.
Your app is generally obligated to support whatever devices are compatible with iOS 13.x, including the iPhone 7/+.
Perhaps if you explained your ask, someone might offer suggestions, etc.