https://tenorshare.com/products/reiboot.html
: The most popular independent database for tracking which iOS versions are still being "signed" (authorized) by Apple. iphone firmware flash tool link
If you want to flash a specific firmware version (as long as it is still "signed" by Apple), you can use an https://tenorshare
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). iphone firmware flash tool link
Similar to ReiBoot, UltFone is a robust Windows-based utility designed to handle critical firmware failures automatically. It is particularly effective for "frozen" screens and boot loops.