Apple only "signs" specific iOS versions (usually the latest ones). Once a version is no longer signed, you cannot normally install or "restore" to it.
Websites and services like shsh.host act as independent, community-driven cloud archives. They allow users to request signatures from Apple while the signing window is open and save those files safely in an external database. Historically, platforms like Cydia's TSS server performed this exact task automatically. Why Saving SHSH Blobs to a Host Matters shsh host
: Historically, it has been used to save blobs for iOS beta firmwares, which some other tools might not support. Core Concept: SHSH Blobs Apple only "signs" specific iOS versions (usually the
“Host is... stable,” Elias said, though his voice sounded layered, as if two people were speaking in near-unison. “The Shsh is resting.” They allow users to request signatures from Apple