Scroll until you see install via Altstore option and select it.
A15 — iPhone 13• You can do it through a series of kernel patches, and it allows you to reach the root of the iOS operating system.
After the process, you can see the checkra1n and Cydia app on your iOS 15 running on your iPhone home screen.
Now it is compatible with iOS 15 RC and all iOS versions iOS 11 to higher.