FlashFire is the spiritual successor to Mobile ODIN. Notes and hints to help you use it: No kernels or recoveries are flashed for FlashFire to run, Android is torn down and restarted in a minimalist manner for the flashing part of the app to run. I’m sure this will completely fail on some devices. A lot(!) of memory is used, likely the entire operation will fail on low-memory devices. I strongly suggest you make an ‘ID’ backup as the very first test and see if that works at all.