That's a common issue with older ASUS boards. You might need to reset your BIOS to factory defaults first, then the option often becomes available to enable.
I’m stuck trying to upgrade from Windows 10 to 11. The PC Health Check app says my computer doesn’t meet the requirements because “Secure Boot” isn’t enabled. I went into my BIOS (UEFI) but the option is greyed out and I can’t turn it on. My motherboard is an older ASUS model. Has anyone else faced this? Is there a way to enable it, or am I just out of luck for Windows 11?
This. Yeah, that's a common snag with older boards. Sometimes you have to switch the BIOS from CSM/Legacy mode to UEFI first, then Secure Boot becomes available.