As of Windows 10 version 2004, the User must enter username and password checkbox no longer appears in the netplwiz tool, which is recommended in many tutorials on the net for automatic logon. There are a total of two ways to re-enable automatic login.
No checkbox for login
1. user is connected to Microsoft account
Go to Settings -> Accounts -> Login options
Hello login required
Disable the Windows Hello login required for Microsoft accounts switch (Off position).
Hello login required disabled
Now start netplwiz via Windows + R.
Run Dialog
Select the user with which automatic login should happen.
Select User
Uncheck the User must enter username and password checkbox and click OK.
Deselect checkbox
Now enter the password of the selected user with which the automatic login should run.
Enter password
After restarting, Windows will now start automatically with the selected user.
2. Local user without Microsoft account
In this case the way is via registry editor.
Start regedit via Run dialog with Windows + R.
Start Registry Editor.
Navigate to the HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\PasswordLess\Device node.
Navigate to (or paste) Device node
Double click on the entry DevicePasswordLessBuildVersion.
Change the value to 0.
Set value to 0
Now start netplwiz via Windows + R.
Run Dialog
Select the user with which automatic login should happen.
Select User
Uncheck the User must enter username and password checkbox and click OK.
Deselect checkbox
Now enter the password of the selected user with which the automatic login should run.
Enter password
After restarting, Windows will now start automatically with the selected user.
Enabling automatic login up to version 1908
For Windows 10 1908 or earlier, automatic login can be enabled directly in the netplwiz tool.
Launch the Run dialog by pressing the key combination Windows + R.
Run Dialog
Type netplwiz here and click OK.
User accounts enabled dialog
Select the user with which automatic login should happen.
Uncheck the User must enter username and password checkbox and click OK.
User accounts dialog disabled
Now enter the password of the selected user with which the automatic login should run.
Dialog user accounts disabled
After restarting, Windows will now start automatically with the selected user.