Updated: Nov 6, 2019
...then this is how you disable it:
Info' below is a copy and paste because I don't want to lose it if the source web site goes away for any reason...
How to disable Simplified Account Creation in Outlook 2016
To disable the Simplified Account Creation dialog box in Outlook 2016 and use the traditional account dialog box instead, follow these steps.
Backup your windows registry or create a retore point - https://support.microsoft.com/en-au/help/322756/how-to-back-up-and-restore-the-registry-in-windows
Start Registry Editor. To do this, use one of the following procedures, as appropriate for your version of Windows.
Windows 10, Windows 8.1 and Windows 8: Press Windows Key + R to open the Run dialog box. Type regedit.exe, and then click OK.
Windows 7: Click Start, type regedit.exe in the search box, and then press Enter.
In Registry Editor, locate and then click the user settings subkey in the registry:
or the group policy subkey in the registry: HKEY_CURRENT_USER\SOFTWARE\Policies\Microsoft\Office\16.0\Outlook\setup
Point to New on the Edit menu and then DWORD (32-bit) Value.
Type DisableOffice365SimplifiedAccountCreation, and then press Enter.
Right-click DisableOffice365SimplifiedAccountCreation, and then select Modify.
In the Value data box, type 1, and then click OK.
On the File menu, select Exit to exit Registry Editor.