Outlook 2019 won't autodiscover and keeps prompting for password with on-prem Exchange.

If you have your domain associated with an Office 365 account, Outlook will completely ignore autodiscover and try to authenticate to Office 365.

Open RegEdit

Navigate to HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Outlook\AutoDiscover 

New DWORD entry, ExcludeExplicitO365Endpoint -  value of 1.

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You are using a SAML provider and get a white blank screen or a ghost login screen-

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity]

"DisableADALatopWAMOverride"=dword:00000001

If the above key change alone does not work, edit this additional Registry key:

[HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity] 

"DisableAADWAM"=dword:00000001

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