How to add a user from the command line in macOS?
A similar tool to useradd is /usr/sbin/sysadminctl on macOS . There isn't a manual but /usr/sbin/sysadminctl -h is explanatory. You should be aware that the command and options will be stored in your shell's history. Note the last line of the help output so that the user password is not stored in your shell's history.