With 6.7, vicfg- is fully deprecated. Refer to the below release notes under 'Feature and Support Notice' -
vSphere Command-Line Interface 6.7 Release Notes
For creating a new user, you have to use the esxcli command. For e.g. creating a user with the username 'TestUser' -
esxcli system account add –id TestUser –password ABC@123 –password-confirmation ABC@123
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Cheers,
Supreet