Installing Previous Firmware in iPhone | New Firmware keeps Rebooting iPhone After upgrading to iOS 14.4.2 my iphone keeps rebooting every 5 mins! I would like to restore my iphone to iOS 14.3.7. After finding signed firmware I tried using iTunes but kept getting error 9 . I found the solution in iFixit where Barry's answers stated that (in short) this is Apples way of giving trouble by removing signed firmware! However he suggested a solution that utilizes paid version of the software to flash earlier version of firmware (ISPW) into iphone, using Reiboot
Now my iphone is completely unlocked, with my account signed in and everything is legit, yet if I restore earlier ISPW, then iTunes keep giving me error that I cant install old firmware! I need to know if there are any free tools online or Github project that can flash old firmware into iPhone? or anyway to check what is causing kernel panic.
When I say old firmware i mean just one step earlier revision where my iphone didnt keep rebooting!

(update 1) iOS 14.4.2 is known to have heating issue which is perhaps why my iphone is rebooting - source
If I have to be honest (and it’s really neat that you are doing this), you probably shouldn’t install previous firmware. It’s probably rebooting for a reason. There might be some broken blocks or code. It could also be infected, possibly malware or an app that uses your device for Crypto Mining. It could also be your device. Please let me know if this helps!