"Disk User" Showing up on EFI boot screen after a clean install with APFS Encryption

- Can someone please enlighten as to what has happened, did I do something wrong?

- Is there a way to correct this behavior, it doesn't seem like Disk user should be exposed in this way

You did nothing wrong if the system drive is an SSD. The only way to correct this is to not encrypt the drive prior to installing the OS. See the last paragraph below. It has nothing to do with APFS format or HFS+ format. I can't explain why you see the Disk User along with User accounts like your screenshot. It may have something to do with formatting your HDD (instead of SSD) drive as APFS. HDDs and Fusion Drives are not currently supported for APFS formatting - only SSDs. If you did this on an HDD, John Galt's advice at the end of his post is what you have to do. Keep your HDD as an HFS+ format.

Anytime you format/encrypt your system drive prior to installing the OS, you will always have the Disk User with a password you set. It's the only way to unlock the system drive after a restart since there were no Users setup prior to encrypting.

If you just format the drive, install the OS, add User accounts and then turn on FileVault to encrypt your drive you will have the opportunity to select the Users you wish to use for unlocking the drive at restart. And there will be no Disk User. When you select one of these Users at the login screen, it will unlock the drive (progress bar will show) and afterwards you will see that User's Desktop.

Maybe you could open Disk Utility and take some snaps to post so we can see what you see. And just for my clarification your computer uses an SSD, not an HDD?

To Post A Screen Shot

1. Press Command-Shift-4 which will change the cursor to crosshairs.
2. Hold down the mouse button and use the crosshairs to select the part of the screen you wish to capture.
3. Release the mouse button and the image will be saved to your Desktop.
4. Click on the Camera icon in the toolbar of the forum message editor.
5. Drag the image onto the Choose File button and click on the Insert button.

The reason for your installation difficulties is almost certainly due to overthinking the installation. No one at Apple expected or would have tested the High Sierra upgrade on anything other than an HFS+ formatted volume, so by prematurely converting it to APFS you only brought misery upon yourself. Instructions to do that do not exist. The HS installer would have detected the presence of a solid state startup drive, and proceeded to converted it to APFS. That's how it's designed to work. Since the conversion was already accomplished no one knows what would have happened.

- Is there a way to correct this behavior, it doesn't seem like Disk user should be exposed in this way

Restore your Mac to a Time Machine or equivalent backup created prior to upgrading, then upgrade in the usual manner.

If as you previously stated this is an SSD drive then you did nothing wrong. APFS is supported on SSDs and HDDs but not Fusion Drives. I would take exception to John Galt's and part of Keg's claims that APFS isn't usable and that you should only use HFS+. I have been using an APFS formatted SSD as my startup drive since the release of High Sierra. As of today, Apple does not recommend using APFS on external HDDs but APFS will work. Just don't use it on Fusion Drives.