As a User setting in the Registry Editor:
HKEY_CURRENT_USER\SOFTWARE\Microsoft\Office\16.0\Outlook\setup
DWORD (32-bit) Value / DisableOffice365SimplifiedAccountCreation=1
or the Group Policy subkey in the registry:
HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\setup
DWORD (32-bit) Value / DisableOffice365SimplifiedAccountCreation=1