1. regedit
  2. HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\SignIn
    15.0 for Office 2013, 16.0. for Office 2016
  3. Since you’re facing the issue, in the right pane of above mentioned key, you’ll see the SignInOptions named registry DWORD (REG_DWORD). It must be showing the Value data equals to 3, double click on this DWORD to modify:

https://www.thewindowsclub.com/sign-in-feature-disabled-office