Starting with Kali 2020.1, there is no longer a superuser account and the default user is now a standard, non-privileged user. In Kali Linux 2020.1, both the default username and password are “kali”
If you would like to use root instead of the none superuser account kali, here are the instructions to do so:
Issue command “sudo su”
<Enter the password for kali user account>
Issue command “passwd root”
<Enter new password and retype that password>
At this point you can log-off and re log-in or you can just switch the user and log in as root.
Let me know if this helped you.