Hello
On your computer, can you please type regedit in the search on the taskbar and press enter to launch Registry Editor, then go to this path:
Computer\HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\Identities
Under the Identities folder on the left pane, do you see folder named after your email address? If so, right click and delete it.
Restart Outlook, and see if you can add it this time.