Legacy FileVault and macOS 10.13
Mike Peterson (via John Gordon):
macOS 10.13 officially kills off support for legacy FileVault. It’s simply not usable with the operating system. If you have High Sierra installed, you won’t see the option to toggle FileVault (see above).
Because of that, users can’t even install macOS 10.13 without first disabling legacy FileVault. But, of course, bugs can happen.
[…]
As indicated in a recent Macworld article, if macOS 10.13 is installed on a system, any active legacy FileVault drives or user accounts become unusable.
