If the system.img was repacked incorrectly, the digital signature will fail.
Best,
You cannot flash an older OS version than what was previously installed. blackberry keyone stuck in bootloader menu repack
Getting your BlackBerry KEYone out of a bootloader loop usually requires returning to basics: a clean, official Autoloader and a stable USB connection. Avoid "repacks" from unverified sources, as these often lack the necessary signatures to pass the KEYone's secure boot check. If the system
Download and install the official drivers so your PC recognizes the phone in "Fastboot" mode. If the system.img was repacked incorrectly