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