UNCLEAR: Root User Account Kali Linux/Raspberry Pi 3 B+ (Change?/How to Change?)

Hello to all,

I've been spending substantial time in trying to get a clear response to the following question from videos around the web, without success:

1) Using a Raspberry Pi 3 B+ with Kali Linux installed, can the root username be changed? The operating system itself warns that the root account is being used and that it represents a security risk. If it can or should be done, I've tried doing so via the "visudo" command, trying to modify users through "usermod -l" command, by trying to "adduser", all without success. Your step by step guidance would be greatly appreciated!

2) I'm unclear if this is a related problem, but adding users is also not working for me. Meaning, the system acknowledges their creation, but when I try to login using the username and password given, the login page "tries to login" and without any "error prompt" simply "reboots" to the same login page with all labels blank. I'd like to make sure what is wrong, regardless of the fact that the user is not a "sudo" user.

Thank you!