Boot From Recovery Drive __exclusive__ -

Intel architectures rely on standard keyboard combinations intercepted during firmware initialization. Shut down the Mac. Connect the recovery drive.

Plug the recovery drive directly into a primary motherboard port (rear ports on desktops) rather than an external USB hub. boot from recovery drive

Automatically scans and replaces missing system BCD/boot files. boot from recovery drive

The process requires a bootable USB drive (which you should have created previously using tools like "Create a recovery drive" in Windows or Recovery Disk Assistant in macOS). boot from recovery drive