Short Answer 
To fix the ‘This version of Vanguard requires secure boot’ error, restart your PC and enter the BIOS/UEFI settings, typically by pressing F2, F10, Del, or Esc. Enable the Secure Boot option and ensure your boot mode is set to UEFI, then save the changes and restart your computer for Vanguard to recognize the new settings.
Step 1: Access BIOS/UEFI Settings
To resolve the error message ‘This version of Vanguard requires secure boot,’ you need to restart your PC and enter the BIOS/UEFI settings. This is typically done by pressing specific keys like F2, F10, Del, or Esc right after you power on your computer. Timing is crucial; be ready to press the key you need as soon as the manufacturer’s logo appears.
Step 2: Enable Secure Boot
Once you are in the BIOS/UEFI settings, locate the Secure Boot option. This feature ensures that your system only boots with trusted firmware. You may need to navigate to a tab like Boot or Security to find this setting. If Secure Boot is disabled, enable it, and ensure that your boot mode is set to UEFI, not Legacy or CSM.
Step 3: Save Changes and Restart
After making the changes to enable Secure Boot, save your settings before exiting the BIOS/UEFI. This is usually done by pressing a specific key such as F10 or choosing an option to Save and Exit. Your computer will restart with the new configurations, and if everything is set correctly, Vanguard will recognize that Secure Boot is enabled, allowing you to launch the game without issue.