Windows 10 connection to Microsoft account is very borked. How to fix or remove it?

I sign in to Win 10 with the Microsoft account [me]@outlook.com. It logs in, but many things don't work right. I've tried every remedy I can find online (except nuking the user and starting over), with no luck.

I'd like to end up with a fully functional, MS-sign-in user account, without losing all my data, settings, etc. from the existing user.

Symptoms

• It doesn't show my real name on the login screen or in Settings, just my account email, as in this question and all of these people.
• In Settings > Accounts > Sync your settings, the main toggle is off and grayed out, and a yellow error reads: Some Windows features are only available if you are using a Microsoft account or work account.
  Note that I am (apparently) using a Microsoft account. I am not on AD or Azure, as most of these folks are.
• In Settings > Accounts > Sign-in options, clicking Password > Change brings up a dialog box which promptly disappears.
  Clicking PIN > Add does nothing at all.
• Using the microsoftaccounts.diagcab troubleshooter from here ends with Microsoft account required. You need a Microsoft account to sync your settings.
  That leads me to think that Windows in some sense hasn't registered my MS account.
• When I try Settings > Accounts > Your info > Sign in with a local account instead, I can go through the little wizard, but it ends with We're sorry, but something went wrong. Your Microsoft account wasn't changed to a local account. Code: 0x80004005
  This is the real kicker, because un-linking the MS account seems to be a fix for all these other symptoms.

Stuff I've tried

• Setting my user's Full name in lusrmgr.msc. It affected the name display on the login screen temporarily, but then it blanked out, and the display went back to the account email.
• Removing the [me]@outlook.com credentials from Credential Manager.
• Deleting all the [me]@outlook.com registry keys. (There were no other accounts in neighboring keys.)
• Changing the MS account password.
• Clean boot and safe mode.
• Creating a new local user and signing in with [me]@outlook.com. It stopped me, saying that account already existed on this computer.
• Signing in and out of other MS-linked things like Cortana, One Drive, and Store.
• Signing in and out and rebooting, x1000.
• sfc and dism
• Windows update
• Removing the device at https://account.microsoft.com/devices
  It hasn't come back, though I've logged in with the account. That also suggests to me that Windows is somehow not really connecting with the account.
• Everything else in every google result for every variation of every symptom.
• Banging my head on the desk.

Details

• I'm on Windows 10 Enterprise, v. 1709, build 16299.192.
• I have local admin and total control over the PC.
• My network connectivity is fine. I can log into the MS account on websites just fine.
• The computer used to be on an AD domain, and I logged in with a domain user. I've since left the domain (on a workgroup now, and a new user) and refreshed the PC.
• As far as I'm aware, [me]@outlook.com has always been the primary account email. There is no other alias to switch back to, as some people suggest.