Hide "disk password" login option at EFI (Filevault) login screen
I have the same problem when booting from an external drive, but not my internal drive!

When I boot normally, I only see a one FileVault option: me. However, when booting from my USB drive, I see two: me, and "Disk Password".

Investigating with fdesetep (sudo fdesetup list —extended) shows that the internal drive has:

ESCROW  UUID                                                                     TYPE USER
        BCF2ABC6-40F8-4F31-A508-7284BC85E65A                   Personal Recovery User
        2EE7445C-13C0-497D-AD54-DA1B8D22A0F7                                  OS User ben


However, the external drive has:

ESCROW  UUID                                                                     TYPE USER
        EB313C9F-E27C-41D5-9EE3-192490C792BE                     Disk Passphrase User
        92ACE5CE-7187-44DB-92CE-56344C18568D                                  OS User ben


Note that the external drive doesn't have a recovery key set (confirmed with fdesetup haspersonalrecoverykey returning false).

It looks like it should be possible to remove the Disk Passphrase using fdesetup, by doing fdesetup remove --uuid &lt;the UUID of Disk Passphrase&gt;. I would strongly recommend adding a recovery key, if you do this.