To restore the use of the F8 key, connect your USB keyboard directly to the computer's USB port.
Apple Thunderbolt Display (27-inch): F8 key does not work using Windows with USB keyboard connected to display
You may notice that when using Windows and a USB keyboard that is connected to a Mac via the USB port on an Apple Thunderbolt Display (27-inch), the F8 key is not recognized by Windows when you attempt to accept the Terms and Conditions agreement or start up into Windows Safe Mode.
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