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When fast boot is enabled, USB devices and drivers won't be available until after OS boot, therefore, the behavior you are describing (fails to update BIOS using F7 or getting to the BIOS) is expected.
On the other hand, I tried to replicate the issue using the express BIOS update (.exe) from the OS and I was able to update the BIOS.
In this case, I would recommend disabling fast boot (per your workaround) as it is the correct process to follow.
Hope this information helps.