Yes there's something called Bitlocker To Go which I believe is
developed by Microsft.
https://www.m3datarecovery.com/mac-bitlocker/bitlocker-to-go-reader-for-mac-osx.html
If you have a backup of your data then perhaps reformat the drive and
try again? As part of the installation High Sierra checks the volume for
errors before doing the installation.
I used to work at the Apple Store as a genius and I can confirm it's
definitely possible for them to unlock it for you. Just like @jgrubbs
mentioned earlier, the will create a binary boot file that can be used
to clear the firmware password.
