Huh, today I learned. I'll consider myself lucky I didn't come across one of these machines yet.
The fast boot involves skipping a bunch of slower pathways using saved knowledge of minimal set of devices to bring up to boot the OS in happy path, and only reset to "slow path" if it fails.
In fast boot, you're often unable to hit the button to enter the menu and at most get to it through windows "reboot to firmware" option.