Restart your PC and enter the BIOS/UEFI setup
Switch the boot mode to UEFI if it is set to Legacy or CSM
Disable CSM/Legacy Boot
Enable Secure Boot in the BIOS/UEFI settings
If prompted, install or load the default Secure Boot keys
Save changes and exit BIOS/UEFI
Boot into Windows
Open System Information and confirm:
BIOS Mode shows UEFI
Secure Boot State shows On
If Secure Boot is still unavailable, convert the system disk from MBR to GPT if needed
Relaunch Battlefield 6 after Secure Boot is enabled