Unfortunately it will have created a new user on disk "John_xyz" instead of "John" where everything used to be stored, and none of your settings or apps will remain.
Note this will fail because of an error with the TPM - might be related to the original bug?.
Follow the first-sign-on steps, including being offered to setup a PIN number.
Booting into safe mode also results in the same. When you click the mouse button or keyboard, the screen darkens as if the username and password boxes are going to appear but they don't.
Logoff and log back in as one of your Azure Domain users. The desktop PC loads to the Windows Login Screen.
After PC restarts, connect device back to Azure Domain.
With that user account "disconnect" the device from your Azure Domain.
Once logged into the desktop, create another temporary user account.
Using a recovery USB stick, enable the local admin account using a regedit.
My solution in the end required the following steps: My colleague also had a related Azure AD-Join problem after Anniversary update, indicating it might be a TPM-related issue. There is clearly a horrible bug in Windows Anniversary Update and Azure AD, because I have found other people online complaining of this exact problem.