Do you mean at computer startup or Windows logon?
We you using a local account without a password and now being forced to login with a Microsoft account with a password? Check your account settings to see what's changed after the update.
You may still be able to auto logon using the steps below, but I would setup a PIN instead if the password is too complex. Or is this a HTPC or shared or shared computer?
For logon check the settings in Registry at HKLM\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
AutoAdminLogon = 1
DefaultUserName =
DefaultPassword = (You may need to create this)
Another tool I used in combination with the above Registry settings is "netplwiz", sometimes the user setting to use a password is enabled, you need to uncheck this.