hello sindarin,
as you may know…
l4t_initrd_flash it took binary files under $OUT/Linux_for_Tegra/tools/kernel_flash/images/ to flash onto your Orin Nano target.
however, it’s flash script to perform sign/encrypt to convert eks_t234.img as eks_t234_sigheader.img.encrypt format
in order to confirm you’ve update EKS image correctly, please see-also Topic 270934 for steps to re-flash the target.