Without a functional SHSH host, downgrading an iDevice to an unsigned iOS version is impossible.
Before using the site, you need exact details about your device: shsh host
Old giants like Cydia’s built-in SHSH hosting (Saurik’s server) are gone. Today, you often need to self-host. Without a functional SHSH host, downgrading an iDevice
To ensure your iOS device remains downgrade-ready, you must save its SHSH blobs while Apple is actively signing the firmware. YouTube·iMAT - Tutorials Without a functional SHSH host