Apple "signs" firmware versions. You generally cannot flash an older version of iOS once Apple has stopped signing it (usually a few weeks after a new update).
Using iTunes or Finder is the only method officially supported by Apple. These tools automatically verify the firmware signature (SHSH blobs) with Apple’s servers. If the firmware is unsigned (Apple stopped allowing it), the flash will fail safely without bricking your phone. iphone firmware flash tool link
If your phone is stuck in a boot loop or you need more control over the flashing process, these tools are widely used by the community: Apple "signs" firmware versions
Apple "signs" firmware versions. You generally cannot flash an older version of iOS once Apple has stopped signing it (usually a few weeks after a new update).
Using iTunes or Finder is the only method officially supported by Apple. These tools automatically verify the firmware signature (SHSH blobs) with Apple’s servers. If the firmware is unsigned (Apple stopped allowing it), the flash will fail safely without bricking your phone.
If your phone is stuck in a boot loop or you need more control over the flashing process, these tools are widely used by the community: