For a volume formatted as CoreStorage on macOS 10.12 or higher

  1. Run this command.

    diskutil cs unlockVolume <lvUUID> -passphrase <personal recovery key>

  2. The user interface shows a prompt to allow access. Enter the keychain password.

    The volume is now unlocked.

  3. Start the decryption. Run.

    diskutil cs decryptVolume <lvUUID>

  4. When prompted, enter the password for the local user.
  5. To monitor progress of the decryption, run.

    diskutil cs list

The user can now reboot the Mac normally. They do not see the FileVault pre-boot screen.