Issue with activating Secure Boot: "Secure variable update is locked down"

[regularlyprosecutor]

I've tried enabling "Secure Boot" in the BIOS as Valorant is now requiring it. When I access the BIOS, I disable CSM Support and enter the Secure Boot menu to enable Secure Boot. However, it shows "Not Active." To resolve this, I change the secure boot mode from "Standard" to "Custom" and then back to "Standard." A message prompts me to install Factory Default Keys, which I accept, but then I receive the message "Secure variable update is locked down" and to "Try again after a system reboot." Despite resetting the PC multiple times, the message persists.