Without boot9.bin , any decryption attempt fails because the BootROM keys are missing.
If you already have boot9strap installed, you can use one of these methods: Boot9.bin 3ds
No system update from Nintendo could fix it because the vulnerability wasn't in the software; it was in the immutable hardware (the BootROM). The only way to remove boot9strap from a 3DS is to physically replace the CPU. Without boot9